Re: [DISCUSS] Developing an "Arrow Compute IR [Intermediate Representation]" to decouple language front ends from Arrow-native compute engines

[Phillip Cloud <cp...@gmail.com>]

Hey everyone,

As many of you know, the compute IR project has a lot of interested parties
and has generated a lot of feedback. In light of some of the feedback we’ve
received, we want to stress that the specification is intended to have
input from many diverse points of view and that we welcome folks outside of
the Arrow community. We think there’s immense potential for a compute IR
that multiple projects--including those outside of the Arrow umbrella--can
leverage.

With that in mind, Jacques has been working on something outside of the
Arrow repo that’ll be shared in a few days, that is designed to bring those
viewpoints to bear on the problem of generic relational computation that
lives outside of the Arrow project.

Inside Arrow, we think that a version of the in-development IR
specifications from the last several weeks will add a ton of value by
informing this new effort and would like to continue to move forward with a
work-in-progress IR inside of Arrow for the time being to enable some work
on API development (independent of exactly how things are serialized) to
take place. It is very likely that we will adopt this broader specification
once the dust has settled, so the format inside of Arrow will be relatively
unstable for a while and not have backwards compatibility guarantees for
now.

The primary focus of the Arrow IR will be on shoring up APIs (producers and
consumers), and we will also be moving the compute IR flatbuffers files out
the format directory into another top-level directory in the repo.

Thanks,
Phillip

On Mon, Aug 30, 2021 at 7:30 PM Weston Pace <we...@gmail.com> wrote:

> My (incredibly naive) interpretation is that there are three problems to
> tackle.
>
> 1) How do you represent a graph and relational operators (join, union,
> groupby, etc.)
>  - The PR appears to be addressing this question fairly well
> 2) How does a frontend query a backend to know what UDFs are supported.
>  - I don't see anything in the spec for this (some comments touch on
> it) but it seems like it would be necessary to build any kind of
> system.
> 3) Is there some well defined set of canonical UDFs that we can all
> agree on the semantics for (e.g. addition, subtraction, etc.)
>  - I thought, from earlier comments in this email thread, that the
> goal was to avoid addressing this.  Although I think there is strong
> value here as well.
>
> So what is the scope of this initiative?  If it is just #1 for example
> then I don't see any need to put types in the IR (and I've commented
> as such in the PR).  From a relational perspective isn't a UDF just a
> black box Table -> UDF -> Table?
>
> On Mon, Aug 30, 2021 at 11:10 AM Phillip Cloud <cp...@gmail.com> wrote:
> >
> > Hey everyone,
> >
> > There's some interesting discussion around types and where their location
> > is in the current PR [1] (and in fact whether to store them at all).
> >
> > It would be great to get some community feedback on this [2] part of the
> PR
> > in particular, because the choice of whether to store types at all has
> > important design consequences.
> >
> > [1]: https://github.com/apache/arrow/pull/10934
> > [2]: https://github.com/apache/arrow/pull/10934/files#r697025313
> >
> > On Fri, Aug 27, 2021 at 2:11 AM Micah Kornfield <em...@gmail.com>
> > wrote:
> >
> > > As an FYI, Iceberg is also considering an IR in relation to view
> support
> > > [1].  I chimed in and pointed them to this thread and Wes's doc.
> Phillip
> > > and Jacques chimed in there as well.
> > >
> > > [1]
> > >
> > >
> https://mail-archives.apache.org/mod_mbox/iceberg-dev/202108.mbox/%3CCAKRVfm6h6WxQtp5fj8Yj8XWR1wFe8VohOkPuoZZGK-UHPhtwjQ%40mail.gmail.com%3E
> > >
> > > On Thu, Aug 26, 2021 at 12:40 PM Phillip Cloud <cp...@gmail.com>
> wrote:
> > >
> > > > Thanks for the feedback Jacques, very helpful. In the latest version
> of
> > > the
> > > > PR, I've tried to incorporate nearly all of these points.
> > > >
> > > > - I've incorporated most of what you had for dereferencing operations
> > > into
> > > > the PR, and gotten rid of schemas except on Read/Write relations.
> > > > - With respect to properties, I've made a bunch more specific
> operators,
> > > > and kept user-defined things special case-y.
> > > > - I haven't incorporated anything close to physical-plan things, but
> I
> > > > think that's a good follow up PR. Having separate representations for
> > > > logical/physical plans seems like a waste of effort ultimately. I
> think
> > > we
> > > > can find a good balance.
> > > > - Agree on UDF support, I think that will have to evolve as the rest
> of
> > > the
> > > > spec evolves. UDFs will need language-dedicated effort given the
> large
> > > > variety of languages that folks will want to use to define functions.
> > > >
> > > > On a separate note, in an effort to move this project forward I'd
> like to
> > > > do one final round of code review from anyone interested and then
> merge
> > > the
> > > > PR after that.
> > > > This spec will be unstable for a while, until we can work out all the
> > > > design kinks and edge cases, and I think getting this initial spec
> in is
> > > > important to start that process.
> > > >
> > > >
> > > > On Mon, Aug 23, 2021 at 1:53 PM Jacques Nadeau <ja...@apache.org>
> > > wrote:
> > > >
> > > > > In a lucky turn of events, Phillip actually turned out to be in my
> neck
> > > > of
> > > > > the woods on Friday so we had a chance to sit down and discuss
> this. To
> > > > > help, I actually shared something I had been working on a few
> months
> > > ago
> > > > > independently (before this discussion started).
> > > > >
> > > > > For reference:
> > > > > Wes PR: https://github.com/apache/arrow/pull/10856
> > > > > Ben PR: https://github.com/apache/arrow/pull/10934
> > > > > Jacques PR: https://github.com/apache/arrow/pull/10979
> > > > >
> > > > > The high level points of feedback I have are:
> > > > >
> > > > >    - Ben PR feels too deconstructed. While I like the elegance and
> > > > >    symmetry, I believe this will lead to substantially more work in
> > > > moving
> > > > >    from serialization format to something closer to what a system
> would
> > > > > want
> > > > >    to manipulate/consume. The reality is that there are a lot of
> really
> > > > > known
> > > > >    things and specializing the representation for these things will
> > > > > ultimately
> > > > >    make things easier to program with without error and easier to
> > > debug.
> > > > > (For
> > > > >    example, imagine trying to inspect a plan in a debugging session
> > > with
> > > > > the
> > > > >    Ben representation.) We should embrace the known things in the
> > > > >    specification.
> > > > >    - I believe that it is a mistake for the inner workings of the
> plan
> > > to
> > > > >    ever use field names. Only input (e.g. file read) and Output
> (e.g.
> > > > > return
> > > > >    to user or write to file) need to have field names. For the
> rest of
> > > > the
> > > > >    system, using field ordinals (determinant whether nested or
> flat) is
> > > > > much
> > > > >    cleaner and is how most execution systems work. For example, in
> > > > Impala I
> > > > >    believe it is called a slot. As I noted in the PR, Calcite as an
> > > > > example is
> > > > >    entirely ordinal based at the algebra level. Rowtypes contain
> field
> > > > > names
> > > > >    but they are actually basically pointless. Field references use
> > > > > RexInputRef
> > > > >    with ordinal based and rules around column order output (e.g.
> what
> > > is
> > > > > the
> > > > >    field order of a join output) are determinant and done entirely
> at
> > > an
> > > > >    ordinal level. The only place where names should be used
> (besides
> > > > >    input/output) is in the case of map keys. In that case, the
> names
> > > are
> > > > >    actually data, as opposed to scheme metadata. This is why I
> propose
> > > a
> > > > >    strongly structured dereference operation [1].
> > > > >    - Properties should only be included in the serialization if
> they
> > > are
> > > > >    not easily re-derivable at plan consumption time. For example,
> > > you'll
> > > > > note
> > > > >    that I don't store schema information for relational operation.
> Each
> > > > >    function and relational operation should already know how a
> given
> > > > input
> > > > > is
> > > > >    transformed to a given output. Capturing this information in the
> > > > > plan/IR is
> > > > >    excessive. In many ways, I compare it to the early use of
> > > VectorLayout
> > > > > [2]
> > > > >    in Arrow schema. It may have provided some additional checksum
> of
> > > the
> > > > >    message but ultimately it caused more pain than it was worth
> (and
> > > thus
> > > > > we
> > > > >    removed it before formalizing the specification). For
> reference, in
> > > > the
> > > > >    context of Dremio, we used to actually do this, send schema
> > > > information
> > > > >    around for all operations. We removed it because in many cases
> > > > becoming
> > > > > the
> > > > >    majority of our internal plan serialization (imagine simple
> > > operations
> > > > > that
> > > > >    are carrying 1000s of fields).
> > > > >    - I suggest focusing on support for both logical and physical
> > > > >    representations. The moment you start talking about optimization
> > > > passes,
> > > > >    many of those would probably be better being done at the logical
> > > > level.
> > > > > The
> > > > >    overlap is really high.
> > > > >    - I think a lot more work must be done before introducing UDFs
> and
> > > > user
> > > > >    defined relational operations. I see one goal being the
> possibility
> > > of
> > > > >    there being three systems: A -> B -> C. A is a IR producer. C
> is a
> > > IR
> > > > >    consumer and B is a IR filter or translator. In this situation,
> B
> > > > > should be
> > > > >    able to operate and do optimizations on a plan even if if there
> are
> > > > > black
> > > > >    box user defined operations. Being able to know the
> > > > > properties-preservation
> > > > >    or not of these operations is important to making decisions. For
> > > > > example,
> > > > >    does a user defined relational operation maintain sortedness?
> > > > > Distribution?
> > > > >    Is a defined UDF idempotent? As such, I think the definition of
> > > those
> > > > > black
> > > > >    boxes should be much more structured. For example: it is a
> python
> > > > >    relational operation named X stored in Y that maintains
> properties
> > > 1,2
> > > > > and
> > > > >    disrupts property 3. Putting just a black box of bytes will
> > > > > substantially
> > > > >    reduce the compatibility and extensibility of the ecosystem of
> tools
> > > > >    working against IR. I'd note that I wouldn't expect this to be a
> > > > burden
> > > > > to
> > > > >    actual end users. By using sensible defaults, I still would
> expect
> > > an
> > > > > end
> > > > >    user tool to support arbitrary user defined operations.
> > > > >    - It might make sense to review the XML representation that Orca
> > > uses
> > > > >    [3]. I haven't looked at it recently but they had a strong goal
> of
> > > > >    decoupling for most of its life (to use in both Greenplum and
> Hawq).
> > > > It
> > > > >    could be the most mature/formal serialization of query plans
> > > > publically
> > > > >    available.
> > > > >
> > > > >
> > > > > [1]
> > > > >
> > > > >
> > > >
> > >
> https://github.com/apache/arrow/pull/10979/files#diff-e40fbc40cf7a131efd2cb098444931774cfad046b8665b38452258ffaa2e3423R34
> > > > > [2]
> > > > >
> > > > >
> > > >
> > >
> https://github.com/apache/arrow/commit/611a4b951e24f4f967c3d382a2027dc035fc37f0
> > > > > [3] https://github.com/greenplum-db/gporca
> > > > >
> > > > >
> > > > > On Tue, Aug 17, 2021 at 11:14 AM Phillip Cloud <cp...@gmail.com>
> > > > wrote:
> > > > >
> > > > > > On Tue, Aug 17, 2021 at 10:56 AM Wes McKinney <
> wesmckinn@gmail.com>
> > > > > wrote:
> > > > > >
> > > > > > > Looking at Ben's alternate PR [1], having an IR that leans
> heavily
> > > on
> > > > > > > memory references to an out-of-band data sidecar seems like an
> > > > > > > approach that would substantially ratchet up the implementation
> > > > > > > complexity as producing the IR would then have the level of
> > > > complexity
> > > > > > > of producing the Arrow IPC format — when producing the "root"
> Plan
> > > > > > > message, you must accumulate a list of the dependent serialized
> > > > > > > submessages, placing the appropriate Buffer memory offset in
> the
> > > Plan
> > > > > > > message, like we do when producing the RecordBatch.buffers
> field.
> > > > This
> > > > > > > seems complicated to me as you must devise a custom binary
> protocol
> > > > to
> > > > > > > concatenate the serialized Plan and the messages it depends on
> > > into a
> > > > > > > single binary payload
> > > > > > >
> > > > > > > <ROOT PLAN>
> > > > > > > <padding>
> > > > > > > <Buffer 0>
> > > > > > > <padding>
> > > > > > > <Buffer 1>
> > > > > > > <padding>
> > > > > > > ...
> > > > > > > <Buffer N - 1>
> > > > > > >
> > > > > > > (one purpose of FlatBufferBuilder is to spare you having to do
> this
> > > > > > > yourself — some reasons we do it for the Arrow IPC format is
> > > because
> > > > > > > appending Arrow memory buffers directly to a FlatBufferBuilder
> > > would
> > > > > > > be inefficient — internal realloc calls — and Flatbuffers are
> > > limited
> > > > > > > to 2GB. Neither of these things are problems here)
> > > > > > >
> > > > > > > In general, I believe the output created by an IR producer
> should
> > > be
> > > > a
> > > > > > > single serialized object without any out-of-band data sidecar —
> > > this
> > > > > > > is much simpler for implementers and we can still provide an
> > > "escape
> > > > > > > hatch" for user-defined operators and functions where the
> required
> > > > > > > function/operator is passed opaquely as an embedded binary
> data.
> > > > > >
> > > > > >
> > > > > >
> > > > > > The serialization format (whether it is Flatbuffers or JSON, or
> > > > > > > something else) should allow for data memoization, so if there
> is a
> > > > > > > user-defined operator/function, or a relation that is used
> multiple
> > > > > > > times throughout the query (potentially with a large schema),
> then
> > > we
> > > > > > > should ensure that the data need not be duplicated in the
> > > > > > > serialization format unnecessarily — in Flatbuffers, you can
> > > achieve
> > > > > > > this by reusing offsets, but we could devise the data
> structures to
> > > > > > > make the memoization of "expensive" objects more explicit.
> > > > > > >
> > > > > >
> > > > > > I think this is something that would need to be explicitly
> encoded in
> > > > > > the structures themselves if it's a hard requirement. I don't
> think
> > > > this
> > > > > > should block
> > > > > > a prototype producer/consumer.
> > > > > >
> > > > > > Is there something in the second PR/design that precludes the
> reuse
> > > of
> > > > > > offsets?
> > > > > > To my eye, the flatbuffers offset reuse mechanism works just as
> well
> > > > > there.
> > > > > >
> > > > > >
> > > > > > > I additionally think that it is important to provide as much
> > > built-in
> > > > > > > support for "canonical" operators/functions (such as the ones
> > > > > > > implemented commonly by SQL engines) as possible, and to
> liberally
> > > > > > > expand the catalogue of "built-in" capabilities. I would still
> > > prefer
> > > > > > > to have large unions/enums of built-in operators/functions and
> to
> > > > > > > expand those unions/enums to accommodate new things when it is
> > > > > > > demonstrated that there is a need to standardize things between
> > > > > > > producers/consumers.
> > > > > > >
> > > > > >
> > > > > > I think there's a middle ground where we add a bit of structure
> > > > > (something
> > > > > > like
> > > > > > a descriptor from the first PR) to indicate whether a thing is
> > > built-in
> > > > > vs
> > > > > > user-defined.
> > > > > > It looks like Ben has pushed something like this to his PR.
> > > > > >
> > > > > > With that scheme, we have both flexibility and a small set of
> special
> > > > > > builtins that make up
> > > > > > a statically typed set for expressions and relational operators.
> > > > > >
> > > > > > I would really like to vet this PR with a prototype this week,
> > > > > > to see whether we need to revisit any major choices. I don't
> think
> > > > we'll
> > > > > be
> > > > > > able to
> > > > > > anticipate all the consequences until we write some code.
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > One of the beneficial properties of the Union/Enum approach
> for the
> > > > > > > operator/function catalogues, is that when there are additions
> to
> > > > > > > those enums, the generated Flatbuffers files will cause many
> > > language
> > > > > > > compilers to warn or error on unhandled enum cases. If all
> > > > > > > function/operator names are strings, then you are essentially
> > > > > > > reimplementing the functionality provided by enums by hand. I
> > > > > > > initially used strings for all function references in my
> original
> > > > > > > prototype, but I now think that using an enum for "built-ins"
> would
> > > > be
> > > > > > > superior (because of the code-generated enum interface) and
> not a
> > > > > > > premature optimization.
> > > > > > >
> > > > > > > [1]: https://github.com/apache/arrow/pull/10934
> > > > > > >
> > > > > > > On Fri, Aug 13, 2021 at 11:26 PM Phillip Cloud <
> cpcloud@gmail.com>
> > > > > > wrote:
> > > > > > > >
> > > > > > > > Hey all,
> > > > > > > >
> > > > > > > > Just wanted to give an update on the effort here.
> > > > > > > >
> > > > > > > > Ben Kietzman has created an alternative proposal to the
> initial
> > > > > design
> > > > > > > [1].
> > > > > > > > It largely overlaps with the original, but differs in a few
> > > > important
> > > > > > > ways:
> > > > > > > >
> > > > > > > > * A big focus of the design is on flexibility, allowing
> > > producers,
> > > > > > > > consumers and ultimately end users of those systems the
> ability
> > > to
> > > > > > define
> > > > > > > > custom operations in the graph.
> > > > > > > > * There are very few predefined relational operations
> (project,
> > > > > filter,
> > > > > > > > join and a handful of others).
> > > > > > > > * There are only 3 types of value expressions: literals,
> field
> > > > > > > references,
> > > > > > > > and function calls.
> > > > > > > > * The model of evaluation is one that requires a final sink
> node,
> > > > to
> > > > > > > > indicate where the record batches from child relations end
> up (a
> > > > > file,
> > > > > > a
> > > > > > > > socket, an in-memory buffer, etc).
> > > > > > > >
> > > > > > > > I've added notes [2] to the original Google doc (under the
> > > > > Alternative
> > > > > > > > Design Notes subheading), and a few pseudocode examples.
> > > > > > > > Unfortunately, these went out of date as soon as Ben pushed
> the
> > > PR
> > > > > [3],
> > > > > > > so
> > > > > > > > I need to update those to reflect his changes. Regardless,
> > > > > > > > the design is broadly the same, so it should still give a
> good
> > > > > > indication
> > > > > > > > of the details of the design.
> > > > > > > >
> > > > > > > > There are a decent number of review comments on the original
> PR
> > > > that
> > > > > I
> > > > > > > plan
> > > > > > > > to port over where they are still relevant.
> > > > > > > > I also plan on adding support for window functions either
> tonight
> > > > or
> > > > > on
> > > > > > > > Monday.
> > > > > > > >
> > > > > > > > Please review this design at your earliest convenience. Since
> > > > > there's a
> > > > > > > > fairly concrete set of types in flatbuffers that
> > > > > > > > we can look at, ideally we can center discussion around the
> > > details
> > > > > in
> > > > > > > the
> > > > > > > > PR.
> > > > > > > >
> > > > > > > > Thanks!
> > > > > > > >
> > > > > > > > [1]: https://github.com/apache/arrow/pull/10856
> > > > > > > > [2]:
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> https://docs.google.com/document/d/1C_XVOG7iFkl6cgWWMyzUoIjfKt-X2UxqagPJrla0bAE/edit#heading=h.4tfbbtaqzu13
> > > > > > > > [3]: https://github.com/apache/arrow/pull/10934
> > > > > > > >
> > > > > > > > On Thu, Aug 12, 2021 at 3:55 PM Julian Hyde <
> > > > jhyde.apache@gmail.com>
> > > > > > > wrote:
> > > > > > > >
> > > > > > > > > > Wes wrote:
> > > > > > > > > >
> > > > > > > > > > Supporting this kind of intra-application engine
> > > > > > > > > > heterogeneity is one of the motivations for the project.
> > > > > > > > >
> > > > > > > > > +1
> > > > > > > > >
> > > > > > > > > The data format is the natural interface between tasks.
> > > (Defining
> > > > > > > “task”
> > > > > > > > > here as “something that is programmed using the IR”.) That
> is
> > > > > Arrow’s
> > > > > > > > > strength.
> > > > > > > > >
> > > > > > > > > So I think the IR should describe what each task should
> do, and
> > > > > tasks
> > > > > > > > > should be fairly small. Not whole relational operators,
> > > operating
> > > > > on
> > > > > > > whole
> > > > > > > > > tables, but pieces of relational operators, operating on
> > > batches
> > > > or
> > > > > > > > > sequences of batches.
> > > > > > > > >
> > > > > > > > > Elsethread, someone mentioned the LoLePop concept and the
> > > > > > > Kohn/Leis/Neuman
> > > > > > > > > paper [1]. The LoLePop concept sounds good for our
> purposes.
> > > > > > > > >
> > > > > > > > > Julian
> > > > > > > > >
> > > > > > > > > [1]
> https://db.in.tum.de/~kohn/papers/lolepops-sigmod21.pdf
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > > On Aug 12, 2021, at 5:19 AM, Wes McKinney <
> > > wesmckinn@gmail.com
> > > > >
> > > > > > > wrote:
> > > > > > > > > >
> > > > > > > > > > On Wed, Aug 11, 2021 at 11:22 PM Phillip Cloud <
> > > > > cpcloud@gmail.com>
> > > > > > > > > wrote:
> > > > > > > > > >>
> > > > > > > > > >> On Wed, Aug 11, 2021 at 4:48 PM Jorge Cardoso Leitão <
> > > > > > > > > >> jorgecarleitao@gmail.com> wrote:
> > > > > > > > > >>
> > > > > > > > > >>> Couple of questions
> > > > > > > > > >>>
> > > > > > > > > >>> 1. Is the goal that IRs have equal semantics, i.e.
> given
> > > > > > > (IR,data), the
> > > > > > > > > >>> operation "(IR,data) - engine -> result" MUST be the
> same
> > > for
> > > > > all
> > > > > > > > > "engine"?
> > > > > > > > > >>>
> > > > > > > > > >>
> > > > > > > > > >> I think that might be a non-starter for mundane reasons:
> > > > there's
> > > > > > > > > probably
> > > > > > > > > >> at least two engines
> > > > > > > > > >> that disagree on the result of sum(x) where x is a
> floating
> > > > > point
> > > > > > > > > column.
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >>> 2. if yes, imo we may need to worry about:
> > > > > > > > > >>> * a definition of equality that implementations agree
> on.
> > > > > > > > > >>> * agreement over what the semantics look like. For
> example,
> > > > do
> > > > > we
> > > > > > > use
> > > > > > > > > >>> kleene logic for AND and OR?
> > > > > > > > > >>>
> > > > > > > > > >>
> > > > > > > > > >> WRT Kleene logic my thoughts are that the IR should
> support
> > > > both
> > > > > > > Kleene
> > > > > > > > > and
> > > > > > > > > >> non-Kleene,
> > > > > > > > > >> and producers can choose their desired semantics.
> > > > > > > > > >>
> > > > > > > > > >> Ibis for example, would override the `&` operator in `a
> & b`
> > > > to
> > > > > > > produce
> > > > > > > > > >> `KleeneAnd(Column(a), Column(b))`.
> > > > > > > > > >>
> > > > > > > > > >>
> > > > > > > > > >>>
> > > > > > > > > >>> To try to understand the gist, let's pick an aggregated
> > > count
> > > > > > over
> > > > > > > a
> > > > > > > > > >>> column: engines often do partial counts over partitions
> > > > > followed
> > > > > > > by a
> > > > > > > > > final
> > > > > > > > > >>> "sum" over the partial counts. Is the idea that the
> query
> > > > > engine
> > > > > > > would
> > > > > > > > > >>> communicate with the compute engine via 2 IRs where
> one is
> > > > > "count
> > > > > > > me
> > > > > > > > > these"
> > > > > > > > > >>> the other is "sum me these"?
> > > > > > > > > >>>
> > > > > > > > > >>> Best,
> > > > > > > > > >>> Jorge
> > > > > > > > > >>>
> > > > > > > > > >>
> > > > > > > > > >> Not in its current incarnation.
> > > > > > > > > >>
> > > > > > > > > >> The idea is that the IR producer communicates a desire
> to
> > > > > count(x)
> > > > > > > to a
> > > > > > > > > >> consumer, and  it's up to the consumer to figure out
> how to
> > > > turn
> > > > > > > that
> > > > > > > > > count
> > > > > > > > > >> into something that makes sense for itself. In your
> example
> > > > > > that's a
> > > > > > > > > series
> > > > > > > > > >> of partial counts followed by a sum.
> > > > > > > > > >>
> > > > > > > > > >
> > > > > > > > > > That said, I think there is a valid use case here where a
> > > > system
> > > > > > > might
> > > > > > > > > > make use of different engines to execute different
> > > (composable)
> > > > > > > layers
> > > > > > > > > > of a complex query.
> > > > > > > > > >
> > > > > > > > > > For example:
> > > > > > > > > >
> > > > > > > > > > * suppose you want to scan and do predicate pushdown on
> an
> > > > > unusual
> > > > > > > > > > data source that is only accessible from one particular
> > > engine
> > > > > but
> > > > > > > > > > * you need to do some analytical operation with the scan
> > > > results
> > > > > > that
> > > > > > > > > > is only supported by another engine
> > > > > > > > > >
> > > > > > > > > > You could decompose the query into two stages with an IR
> > > > > relational
> > > > > > > > > > expression for each stage and use then the engines
> together
> > > to
> > > > > > > > > > accomplish what you need (of course, you would need an
> > > > > > orchestration
> > > > > > > > > > layer to handle plumbing the query engine inputs and
> outputs
> > > > > > together
> > > > > > > > > > as Arrow streams). Supporting this kind of
> intra-application
> > > > > engine
> > > > > > > > > > heterogeneity is one of the motivations for the project.
> > > > > > > > > >
> > > > > > > > > >>>
> > > > > > > > > >>>
> > > > > > > > > >>>
> > > > > > > > > >>>
> > > > > > > > > >>>
> > > > > > > > > >>> On Wed, Aug 11, 2021 at 6:10 PM Phillip Cloud <
> > > > > cpcloud@gmail.com
> > > > > > >
> > > > > > > > > wrote:
> > > > > > > > > >>>
> > > > > > > > > >>>> Thanks Wes,
> > > > > > > > > >>>>
> > > > > > > > > >>>> Great to be back working on Arrow again and engaging
> with
> > > > the
> > > > > > > > > community.
> > > > > > > > > >>> I
> > > > > > > > > >>>> am really excited about this effort.
> > > > > > > > > >>>>
> > > > > > > > > >>>> I think there are a number of concerns I see as
> important
> > > to
> > > > > > > address
> > > > > > > > > in
> > > > > > > > > >>> the
> > > > > > > > > >>>> compute IR proposal:
> > > > > > > > > >>>>
> > > > > > > > > >>>> 1. Requirement for output types.
> > > > > > > > > >>>>
> > > > > > > > > >>>> I think that so far there's been many reasons for
> > > requiring
> > > > > > > > > conforming IR
> > > > > > > > > >>>> producers and consumers to adhere to output types,
> but I
> > > > > haven't
> > > > > > > seen
> > > > > > > > > a
> > > > > > > > > >>>> strong rationale for keeping them optional (in the
> > > semantic
> > > > > > > sense, not
> > > > > > > > > >>> WRT
> > > > > > > > > >>>> any particular serialization format's representation
> of
> > > > > > > optionality).
> > > > > > > > > >>>>
> > > > > > > > > >>>> I think a design that includes unambiguous semantics
> for
> > > > > output
> > > > > > > types
> > > > > > > > > (a
> > > > > > > > > >>>> consumer must produce a value of the requested type or
> > > it's
> > > > an
> > > > > > > > > >>>> error/non-conforming) is simpler to reason about for
> > > > > producers,
> > > > > > > and
> > > > > > > > > >>>> provides a strong guarantee for end users (humans or
> > > > machines
> > > > > > > > > >>> constructing
> > > > > > > > > >>>> IR from an API and expecting the thing they ask for
> back
> > > > from
> > > > > > the
> > > > > > > IR
> > > > > > > > > >>>> consumer).
> > > > > > > > > >>>>
> > > > > > > > > >>>> 2. Flexibility
> > > > > > > > > >>>>
> > > > > > > > > >>>> The current PR is currently unable to support what I
> think
> > > > are
> > > > > > > killer
> > > > > > > > > >>>> features of the IR: custom operators (relational or
> > > column)
> > > > > and
> > > > > > > UDFs.
> > > > > > > > > In
> > > > > > > > > >>> my
> > > > > > > > > >>>> mind, on top of the generalized compute description
> that
> > > the
> > > > > IR
> > > > > > > > > offers,
> > > > > > > > > >>> the
> > > > > > > > > >>>> ability for producers and consumers of IR to extend
> the IR
> > > > > > without
> > > > > > > > > >>> needing
> > > > > > > > > >>>> to modify Arrow or depend on anything except the
> format is
> > > > > > itself
> > > > > > > > > >>> something
> > > > > > > > > >>>> that is necessary to gain adoption.
> > > > > > > > > >>>>
> > > > > > > > > >>>> Developers will need to build custom relational
> operators
> > > > > (e.g.,
> > > > > > > > > scans of
> > > > > > > > > >>>> backends that don't exist anywhere for which a user
> has
> > > code
> > > > > to
> > > > > > > > > >>> implement)
> > > > > > > > > >>>> and custom functions (anything operating on a column
> that
> > > > > > doesn't
> > > > > > > > > already
> > > > > > > > > >>>> exist, really). Furthermore, I think we can actually
> drive
> > > > > > > building an
> > > > > > > > > >>>> Arrow consumer using the same API that an end user
> would
> > > use
> > > > > to
> > > > > > > extend
> > > > > > > > > >>> the
> > > > > > > > > >>>> IR.
> > > > > > > > > >>>>
> > > > > > > > > >>>> 3. Window Functions
> > > > > > > > > >>>>
> > > > > > > > > >>>> Window functions are, I think, an important part of
> the IR
> > > > > value
> > > > > > > > > >>>> proposition, as they are one of the more complex
> operators
> > > > in
> > > > > > > > > databases.
> > > > > > > > > >>> I
> > > > > > > > > >>>> think we need to have something in the initial IR
> proposal
> > > > to
> > > > > > > support
> > > > > > > > > >>> these
> > > > > > > > > >>>> operations.
> > > > > > > > > >>>>
> > > > > > > > > >>>> 4. Non relational Joins
> > > > > > > > > >>>>
> > > > > > > > > >>>> Things like as-of join and window join operators
> aren't
> > > yet
> > > > > > > fleshed
> > > > > > > > > out
> > > > > > > > > >>> in
> > > > > > > > > >>>> the IR, and I'm not sure they should be in scope for
> the
> > > > > initial
> > > > > > > > > >>> prototype.
> > > > > > > > > >>>> I think once we settle on a design, we can work the
> design
> > > > of
> > > > > > > these
> > > > > > > > > >>>> particular operators out during the initial
> prototype. I
> > > > think
> > > > > > the
> > > > > > > > > >>>> specification of these operators should basically be
> PR #2
> > > > > after
> > > > > > > the
> > > > > > > > > >>>> initial design lands.
> > > > > > > > > >>>>
> > > > > > > > > >>>> # Order of Work
> > > > > > > > > >>>>
> > > > > > > > > >>>> 1. Nail down the design. Anything else is a
> non-starter.
> > > > > > > > > >>>>
> > > > > > > > > >>>> 2. Prototype an IR producer using Ibis
> > > > > > > > > >>>>
> > > > > > > > > >>>> Ibis is IMO a good candidate for a first IR producer
> as it
> > > > > has a
> > > > > > > > > number
> > > > > > > > > >>> of
> > > > > > > > > >>>> desirable properties that make prototyping faster and
> > > allow
> > > > > for
> > > > > > > us to
> > > > > > > > > >>>> refine the design of the IR as needed based on how the
> > > > > > > implementation
> > > > > > > > > >>> goes:
> > > > > > > > > >>>> * It's written in Python so it has native support for
> > > nearly
> > > > > all
> > > > > > > of
> > > > > > > > > >>>> flatbuffers' features without having to creating
> bindings
> > > to
> > > > > > C++.
> > > > > > > > > >>>> * There's already a set of rules for type checking, as
> > > well
> > > > as
> > > > > > > APIs
> > > > > > > > > for
> > > > > > > > > >>>> constructing expression trees, which means we don't
> need
> > > to
> > > > > > worry
> > > > > > > > > about
> > > > > > > > > >>>> building a type checker for the prototype.
> > > > > > > > > >>>>
> > > > > > > > > >>>> 3. Prototype an IR consumer in C++
> > > > > > > > > >>>>
> > > > > > > > > >>>> I think in parallel to the producer prototype we can
> > > further
> > > > > > > inform
> > > > > > > > > the
> > > > > > > > > >>>> design from the consumer side by prototyping an IR
> > > consumer
> > > > in
> > > > > > > C++ . I
> > > > > > > > > >>> know
> > > > > > > > > >>>> Ben Kietzman has expressed interest in working on
> this.
> > > > > > > > > >>>>
> > > > > > > > > >>>> Very interested to hear others' thoughts.
> > > > > > > > > >>>>
> > > > > > > > > >>>> -Phillip
> > > > > > > > > >>>>
> > > > > > > > > >>>> On Tue, Aug 10, 2021 at 10:56 AM Wes McKinney <
> > > > > > > wesmckinn@gmail.com>
> > > > > > > > > >>> wrote:
> > > > > > > > > >>>>
> > > > > > > > > >>>>> Thank you for all the feedback and comments on the
> > > > document.
> > > > > > I'm
> > > > > > > on
> > > > > > > > > >>>>> vacation this week, so I'm delayed responding to
> > > > everything,
> > > > > > but
> > > > > > > I
> > > > > > > > > >>>>> will get to it as quickly as I can. I will be at
> VLDB in
> > > > > > > Copenhagen
> > > > > > > > > >>>>> next week if anyone would like to chat in person
> about
> > > it,
> > > > > and
> > > > > > > we can
> > > > > > > > > >>>>> relay the content of any discussions back to the
> > > > > > > document/PR/e-mail
> > > > > > > > > >>>>> thread.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> I know that Phillip Cloud expressed interest in
> working
> > > on
> > > > > the
> > > > > > > PR and
> > > > > > > > > >>>>> helping work through many of the details, so I'm
> glad to
> > > > have
> > > > > > the
> > > > > > > > > >>>>> help. If there are others who would like to work on
> the
> > > PR
> > > > or
> > > > > > dig
> > > > > > > > > into
> > > > > > > > > >>>>> the details, please let me know. We might need to
> figure
> > > > out
> > > > > > how
> > > > > > > to
> > > > > > > > > >>>>> accommodate "many cooks" by setting up the ComputeIR
> > > > project
> > > > > > > > > somewhere
> > > > > > > > > >>>>> separate from the format/ directory to permit it to
> exist
> > > > in
> > > > > a
> > > > > > > > > >>>>> Work-In-Progress status for a period of time until we
> > > work
> > > > > > > through
> > > > > > > > > the
> > > > > > > > > >>>>> various details and design concerns.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> Re Julian's comment
> > > > > > > > > >>>>>
> > > > > > > > > >>>>>> The biggest surprise is that this language does full
> > > > > > relational
> > > > > > > > > >>>>> operations. I was expecting that it would do
> fragments of
> > > > the
> > > > > > > > > >>> operations.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> There's a related but different (yet still
> interesting
> > > and
> > > > > > > worthy of
> > > > > > > > > >>>>> analysis) problem of creating an "engine language"
> that
> > > > > > describes
> > > > > > > > > more
> > > > > > > > > >>>>> mechanically the constituent parts of implementing
> the
> > > > > > relational
> > > > > > > > > >>>>> operators. To create a functional computation
> language
> > > with
> > > > > > > concrete
> > > > > > > > > >>>>> Arrow data structures as a top-level primitive sounds
> > > like
> > > > an
> > > > > > > > > >>>>> interesting research area where I could see something
> > > > > > developing
> > > > > > > > > >>>>> eventually.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> The main problem I'm interested in solving right now
> is
> > > > > > enabling
> > > > > > > > > front
> > > > > > > > > >>>>> ends that have sufficient understanding of relational
> > > > algebra
> > > > > > and
> > > > > > > > > data
> > > > > > > > > >>>>> frame operations to talk to engines without having
> to go
> > > > > > > backwards
> > > > > > > > > >>>>> from their logical query plans to SQL. So as
> mentioned in
> > > > the
> > > > > > > > > >>>>> document, being able to faithfully carry the
> relational
> > > > > > operator
> > > > > > > node
> > > > > > > > > >>>>> information generated by Calcite or Ibis or another
> > > system
> > > > > > would
> > > > > > > be
> > > > > > > > > >>>>> super useful. Defining the semantics of various
> kinds of
> > > > > > > user-defined
> > > > > > > > > >>>>> functions would also be helpful to standardize the
> > > > > > > > > >>>>> engine-to-user-language UDF/extension interface.
> > > > > > > > > >>>>>
> > > > > > > > > >>>>> On Tue, Aug 10, 2021 at 2:36 PM Dimitri Vorona <
> > > > > > > alendit@gmail.com>
> > > > > > > > > >>>> wrote:
> > > > > > > > > >>>>>>
> > > > > > > > > >>>>>> Hi Wes,
> > > > > > > > > >>>>>>
> > > > > > > > > >>>>>> cool initiative! Reminded me of "Building Advanced
> SQL
> > > > > > Analytics
> > > > > > > > > From
> > > > > > > > > >>>>>> Low-Level Plan Operators" from SIGMOD 2021 (
> > > > > > > > > >>>>>>
> http://db.in.tum.de/~kohn/papers/lolepops-sigmod21.pdf)
> > > > > which
> > > > > > > > > >>>> proposes a
> > > > > > > > > >>>>>> set of building block for advanced aggregation.
> > > > > > > > > >>>>>>
> > > > > > > > > >>>>>> Cheers,
> > > > > > > > > >>>>>> Dimitri.
> > > > > > > > > >>>>>>
> > > > > > > > > >>>>>> On Thu, Aug 5, 2021 at 7:59 PM Julian Hyde <
> > > > > > > jhyde.apache@gmail.com>
> > > > > > > > > >>>>> wrote:
> > > > > > > > > >>>>>>
> > > > > > > > > >>>>>>> Wes,
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>>> Thanks for this. I’ve added comments to the doc
> and to
> > > > the
> > > > > > PR.
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>>> The biggest surprise is that this language does
> full
> > > > > > relational
> > > > > > > > > >>>>>>> operations. I was expecting that it would do
> fragments
> > > of
> > > > > the
> > > > > > > > > >>>>> operations.
> > > > > > > > > >>>>>>> Consider join. A distributed hybrid hash join
> needs to
> > > > > > > partition
> > > > > > > > > >>> rows
> > > > > > > > > >>>>> into
> > > > > > > > > >>>>>>> output buffers based on a hash key, build hash
> tables,
> > > > > probe
> > > > > > > into
> > > > > > > > > >>>> hash
> > > > > > > > > >>>>>>> tables, scan hash tables for untouched
> “outer”rows, and
> > > > so
> > > > > > > forth.
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>>> I see Arrow’s compute as delivering each of those
> > > > > operations,
> > > > > > > > > >>> working
> > > > > > > > > >>>>> on
> > > > > > > > > >>>>>>> perhaps a batch at a time, or a sequence of
> batches,
> > > with
> > > > > > some
> > > > > > > > > >>> other
> > > > > > > > > >>>>> system
> > > > > > > > > >>>>>>> coordinating those tasks. So I would expect to see
> > > > Arrow’s
> > > > > > > compute
> > > > > > > > > >>>>> language
> > > > > > > > > >>>>>>> mainly operating on batches rather than a table
> > > > > abstraction.
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>>> Julian
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>>>> On Aug 2, 2021, at 5:16 PM, Wes McKinney <
> > > > > > wesmckinn@gmail.com
> > > > > > > >
> > > > > > > > > >>>>> wrote:
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> hi folks,
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> This idea came up in passing in the past -- given
> that
> > > > > there
> > > > > > > are
> > > > > > > > > >>>>>>>> multiple independent efforts to develop
> Arrow-native
> > > > query
> > > > > > > > > >>> engines
> > > > > > > > > >>>>>>>> (and surely many more to come), it seems like it
> would
> > > > be
> > > > > > > > > >>> valuable
> > > > > > > > > >>>> to
> > > > > > > > > >>>>>>>> have a way to enable user languages (like Java,
> > > Python,
> > > > R,
> > > > > > or
> > > > > > > > > >>> Rust,
> > > > > > > > > >>>>>>>> for example) to communicate with backend computing
> > > > engines
> > > > > > > (like
> > > > > > > > > >>>>>>>> DataFusion, or new computing capabilities being
> built
> > > in
> > > > > the
> > > > > > > > > >>> Arrow
> > > > > > > > > >>>>> C++
> > > > > > > > > >>>>>>>> library) in a fashion that is "lower-level" than
> SQL
> > > and
> > > > > > > > > >>>> specialized
> > > > > > > > > >>>>>>>> to Arrow's type system. So rather than leaving it
> to a
> > > > SQL
> > > > > > > > > >>> parser /
> > > > > > > > > >>>>>>>> analyzer framework to generate an expression tree
> of
> > > > > > > relational
> > > > > > > > > >>>>>>>> operators and then translate that to an
> Arrow-native
> > > > > > > > > >>>> compute-engine's
> > > > > > > > > >>>>>>>> internal grammer, a user framework could provide
> the
> > > > > desired
> > > > > > > > > >>>>>>>> Arrow-native expression tree / data manipulations
> > > > directly
> > > > > > and
> > > > > > > > > >>> skip
> > > > > > > > > >>>>>>>> the SQL altogether.
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> The idea of creating a "serialized intermediate
> > > > > > representation
> > > > > > > > > >>>> (IR)"
> > > > > > > > > >>>>>>>> for Arrow compute operations would be to serve use
> > > cases
> > > > > > large
> > > > > > > > > >>> and
> > > > > > > > > >>>>>>>> small -- from the most complex TPC-* or time
> series
> > > > > database
> > > > > > > > > >>> query
> > > > > > > > > >>>> to
> > > > > > > > > >>>>>>>> the most simple array predicate/filter sent with
> an
> > > RPC
> > > > > > > request
> > > > > > > > > >>>> using
> > > > > > > > > >>>>>>>> Arrow Flight. It is deliberately language- and
> > > > > > > engine-agnostic,
> > > > > > > > > >>>> with
> > > > > > > > > >>>>>>>> the only commonality across usages being the Arrow
> > > > > columnar
> > > > > > > > > >>> format
> > > > > > > > > >>>>>>>> (schemas and array types). This would be better
> than
> > > > > leaving
> > > > > > > it
> > > > > > > > > >>> to
> > > > > > > > > >>>>>>>> each application to develop its own bespoke
> expression
> > > > > > > > > >>>>> representations
> > > > > > > > > >>>>>>>> for its needs.
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> I spent a while thinking about this and wrote up a
> > > brain
> > > > > > dump
> > > > > > > RFC
> > > > > > > > > >>>>>>>> document [1] and accompanying pull request [2]
> that
> > > > makes
> > > > > > the
> > > > > > > > > >>>>> possibly
> > > > > > > > > >>>>>>>> controversial choice of using Flatbuffers to
> represent
> > > > the
> > > > > > > > > >>>> serialized
> > > > > > > > > >>>>>>>> IR. I discuss the rationale for the choice of
> > > > Flatbuffers
> > > > > in
> > > > > > > the
> > > > > > > > > >>>> RFC
> > > > > > > > > >>>>>>>> document. This PR is obviously deficient in many
> > > regards
> > > > > > > > > >>>> (incomplete,
> > > > > > > > > >>>>>>>> hacky, or unclear in places), and will need some
> help
> > > > from
> > > > > > > others
> > > > > > > > > >>>> to
> > > > > > > > > >>>>>>>> flesh out. I suspect that actually implementing
> the IR
> > > > > will
> > > > > > be
> > > > > > > > > >>>>>>>> necessary to work out many of the low-level
> details.
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> Note that this IR is intended to be more of a
> > > "superset"
> > > > > > > project
> > > > > > > > > >>>> than
> > > > > > > > > >>>>>>>> a "lowest common denominator". So there may be
> things
> > > > that
> > > > > > it
> > > > > > > > > >>>>> includes
> > > > > > > > > >>>>>>>> which are only available in some engines (e.g.
> engines
> > > > > that
> > > > > > > have
> > > > > > > > > >>>>>>>> specialized handling of time series data).
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> As some of my personal motivation for the project,
> > > > > > concurrent
> > > > > > > > > >>> with
> > > > > > > > > >>>>> the
> > > > > > > > > >>>>>>>> genesis of Apache Arrow, I started a Python
> project
> > > > called
> > > > > > > Ibis
> > > > > > > > > >>> [3]
> > > > > > > > > >>>>>>>> (which is similar to R's dplyr project) which
> serves
> > > as
> > > > a
> > > > > > > "Python
> > > > > > > > > >>>>>>>> analytical query IR builder" that is capable of
> > > > generating
> > > > > > > most
> > > > > > > > > >>> of
> > > > > > > > > >>>>> the
> > > > > > > > > >>>>>>>> SQL standard, targeting many different SQL
> dialects
> > > and
> > > > > > other
> > > > > > > > > >>>>> backends
> > > > > > > > > >>>>>>>> (like pandas). Microsoft ([4]) and Google ([5])
> have
> > > > used
> > > > > > this
> > > > > > > > > >>>>> library
> > > > > > > > > >>>>>>>> as a "many-SQL" middleware. As such, I would like
> to
> > > be
> > > > > able
> > > > > > > to
> > > > > > > > > >>>>>>>> translate between the in-memory "logical query"
> data
> > > > > > > structures
> > > > > > > > > >>> in
> > > > > > > > > >>>> a
> > > > > > > > > >>>>>>>> library like Ibis to a serialized format that can
> be
> > > > > > executed
> > > > > > > by
> > > > > > > > > >>>> many
> > > > > > > > > >>>>>>>> different Arrow-native query engines. The
> expression
> > > > > > > primitives
> > > > > > > > > >>>>>>>> available in Ibis should serve as helpful test
> cases,
> > > > too.
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> I look forward to the community's comments on the
> RFC
> > > > > > document
> > > > > > > > > >>> [1]
> > > > > > > > > >>>>> and
> > > > > > > > > >>>>>>>> pull request [2] -- I realize that arriving at
> > > consensus
> > > > > on
> > > > > > a
> > > > > > > > > >>>> complex
> > > > > > > > > >>>>>>>> and ambitious project like this can be
> challenging so
> > > I
> > > > > > > recommend
> > > > > > > > > >>>>>>>> spending time on the "non-goals" section in the
> RFC
> > > and
> > > > > ask
> > > > > > > > > >>>> questions
> > > > > > > > > >>>>>>>> if you are unclear about the scope of what
> problems
> > > this
> > > > > is
> > > > > > > > > >>> trying
> > > > > > > > > >>>> to
> > > > > > > > > >>>>>>>> solve. I would be happy to give Edit access on
> the RFC
> > > > > > > document
> > > > > > > > > >>> to
> > > > > > > > > >>>>>>>> others and would consider ideas about how to move
> > > > forward
> > > > > > with
> > > > > > > > > >>>>>>>> something that is able to be implemented by
> different
> > > > > Arrow
> > > > > > > > > >>>> libraries
> > > > > > > > > >>>>>>>> in the reasonably near future.
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> Thanks,
> > > > > > > > > >>>>>>>> Wes
> > > > > > > > > >>>>>>>>
> > > > > > > > > >>>>>>>> [1]:
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > > >>>
> > > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> https://docs.google.com/document/d/1C_XVOG7iFkl6cgWWMyzUoIjfKt-X2UxqagPJrla0bAE/edit#
> > > > > > > > > >>>>>>>> [2]: https://github.com/apache/arrow/pull/10856
> > > > > > > > > >>>>>>>> [3]: https://ibis-project.org/
> > > > > > > > > >>>>>>>> [4]:
> > > > > http://cidrdb.org/cidr2021/papers/cidr2021_paper08.pdf
> > > > > > > > > >>>>>>>> [5]:
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > > >>>
> > > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> https://cloud.google.com/blog/products/databases/automate-data-validation-with-dvt
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>>>
> > > > > > > > > >>>>>
> > > > > > > > > >>>>
> > > > > > > > > >>>
> > > > > > > > >
> > > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
>
>

RE: [DISCUSS] Developing an "Arrow Compute IR [Intermediate Representation]" to decouple language front ends from Arrow-native compute engines

["Yang, Binwei" <bi...@intel.com>]

This is excellent proposal. We worked on apache arrow based native Spark SQL engine offloading for 1.5 years. Currently we extended Gandiva's node and expression definition to pass query plan from Spark to native code. We will try start to try substrait. These features can definitely help:

(O) The plan tree should be human readable, so spark can dump and we can easily check if it's correct
(O) Easily restore the buffer in python. Our optimization flow is: run Spark get hot stage, easily reproduce the whole stage in python/cython, analysis and sample the single stage to optimize it. The inputs to python is 1) data source or shuffled data, 2) the query plan.


Thanks
Binwei

-----Original Message-----
From: Jacques Nadeau <ja...@apache.org> 
Sent: Wednesday, September 8, 2021 07:06
To: dev <de...@arrow.apache.org>
Subject: Re: [DISCUSS] Developing an "Arrow Compute IR [Intermediate Representation]" to decouple language front ends from Arrow-native compute engines

As Phillip mentioned, I think there is something powerful in producing a
standard serialized representation of compute operations beyond just Arrow
and I'd really like to create a broader community around it. This has been
something I had been independently thinking about for the last several
months. The discussion here has inspired me to start making real progress
on this work. As such, I created a new repository and site where I've
started to put together work around a new specification for compute. I
would love for the people here to help define this and will be looking to a
number of other communities to also contribute. One of my goals has been to
break the specification into a number of much smaller pieces [1] so that we
can make progress on each subsection without being overwhelmed by the
amount of content that must be reviewed.

Would love to hear people's ideas on this initiative.

The site is here: https://substrait.io/
The repo is here: https://github.com/substrait-io/substrait

[1] https://substrait.io/spec/specification/#components



On Wed, Sep 1, 2021 at 3:26 PM Phillip Cloud <cp...@gmail.com> wrote:

> Hey everyone,
>
> As many of you know, the compute IR project has a lot of interested parties
> and has generated a lot of feedback. In light of some of the feedback we’ve
> received, we want to stress that the specification is intended to have
> input from many diverse points of view and that we welcome folks outside of
> the Arrow community. We think there’s immense potential for a compute IR
> that multiple projects--including those outside of the Arrow umbrella--can
> leverage.
>
> With that in mind, Jacques has been working on something outside of the
> Arrow repo that’ll be shared in a few days, that is designed to bring those
> viewpoints to bear on the problem of generic relational computation that
> lives outside of the Arrow project.
>
> Inside Arrow, we think that a version of the in-development IR
> specifications from the last several weeks will add a ton of value by
> informing this new effort and would like to continue to move forward with a
> work-in-progress IR inside of Arrow for the time being to enable some work
> on API development (independent of exactly how things are serialized) to
> take place. It is very likely that we will adopt this broader specification
> once the dust has settled, so the format inside of Arrow will be relatively
> unstable for a while and not have backwards compatibility guarantees for
> now.
>
> The primary focus of the Arrow IR will be on shoring up APIs (producers and
> consumers), and we will also be moving the compute IR flatbuffers files out
> the format directory into another top-level directory in the repo.
>
> Thanks,
> Phillip
>
> On Mon, Aug 30, 2021 at 7:30 PM Weston Pace <we...@gmail.com> wrote:
>
> > My (incredibly naive) interpretation is that there are three problems to
> > tackle.
> >
> > 1) How do you represent a graph and relational operators (join, union,
> > groupby, etc.)
> >  - The PR appears to be addressing this question fairly well
> > 2) How does a frontend query a backend to know what UDFs are supported.
> >  - I don't see anything in the spec for this (some comments touch on
> > it) but it seems like it would be necessary to build any kind of
> > system.
> > 3) Is there some well defined set of canonical UDFs that we can all
> > agree on the semantics for (e.g. addition, subtraction, etc.)
> >  - I thought, from earlier comments in this email thread, that the
> > goal was to avoid addressing this.  Although I think there is strong
> > value here as well.
> >
> > So what is the scope of this initiative?  If it is just #1 for example
> > then I don't see any need to put types in the IR (and I've commented
> > as such in the PR).  From a relational perspective isn't a UDF just a
> > black box Table -> UDF -> Table?
> >
> > On Mon, Aug 30, 2021 at 11:10 AM Phillip Cloud <cp...@gmail.com>
> wrote:
> > >
> > > Hey everyone,
> > >
> > > There's some interesting discussion around types and where their
> location
> > > is in the current PR [1] (and in fact whether to store them at all).
> > >
> > > It would be great to get some community feedback on this [2] part of
> the
> > PR
> > > in particular, because the choice of whether to store types at all has
> > > important design consequences.
> > >
> > > [1]: https://github.com/apache/arrow/pull/10934
> > > [2]: https://github.com/apache/arrow/pull/10934/files#r697025313
> > >
> > > On Fri, Aug 27, 2021 at 2:11 AM Micah Kornfield <emkornfield@gmail.com
> >
> > > wrote:
> > >
> > > > As an FYI, Iceberg is also considering an IR in relation to view
> > support
> > > > [1].  I chimed in and pointed them to this thread and Wes's doc.
> > Phillip
> > > > and Jacques chimed in there as well.
> > > >
> > > > [1]
> > > >
> > > >
> >
> https://mail-archives.apache.org/mod_mbox/iceberg-dev/202108.mbox/%3CCAKRVfm6h6WxQtp5fj8Yj8XWR1wFe8VohOkPuoZZGK-UHPhtwjQ%40mail.gmail.com%3E
> > > >
> > > > On Thu, Aug 26, 2021 at 12:40 PM Phillip Cloud <cp...@gmail.com>
> > wrote:
> > > >
> > > > > Thanks for the feedback Jacques, very helpful. In the latest
> version
> > of
> > > > the
> > > > > PR, I've tried to incorporate nearly all of these points.
> > > > >
> > > > > - I've incorporated most of what you had for dereferencing
> operations
> > > > into
> > > > > the PR, and gotten rid of schemas except on Read/Write relations.
> > > > > - With respect to properties, I've made a bunch more specific
> > operators,
> > > > > and kept user-defined things special case-y.
> > > > > - I haven't incorporated anything close to physical-plan things,
> but
> > I
> > > > > think that's a good follow up PR. Having separate representations
> for
> > > > > logical/physical plans seems like a waste of effort ultimately. I
> > think
> > > > we
> > > > > can find a good balance.
> > > > > - Agree on UDF support, I think that will have to evolve as the
> rest
> > of
> > > > the
> > > > > spec evolves. UDFs will need language-dedicated effort given the
> > large
> > > > > variety of languages that folks will want to use to define
> functions.
> > > > >
> > > > > On a separate note, in an effort to move this project forward I'd
> > like to
> > > > > do one final round of code review from anyone interested and then
> > merge
> > > > the
> > > > > PR after that.
> > > > > This spec will be unstable for a while, until we can work out all
> the
> > > > > design kinks and edge cases, and I think getting this initial spec
> > in is
> > > > > important to start that process.
> > > > >
> > > > >
> > > > > On Mon, Aug 23, 2021 at 1:53 PM Jacques Nadeau <jacques@apache.org
> >
> > > > wrote:
> > > > >
> > > > > > In a lucky turn of events, Phillip actually turned out to be in
> my
> > neck
> > > > > of
> > > > > > the woods on Friday so we had a chance to sit down and discuss
> > this. To
> > > > > > help, I actually shared something I had been working on a few
> > months
> > > > ago
> > > > > > independently (before this discussion started).
> > > > > >
> > > > > > For reference:
> > > > > > Wes PR: https://github.com/apache/arrow/pull/10856
> > > > > > Ben PR: https://github.com/apache/arrow/pull/10934
> > > > > > Jacques PR: https://github.com/apache/arrow/pull/10979
> > > > > >
> > > > > > The high level points of feedback I have are:
> > > > > >
> > > > > >    - Ben PR feels too deconstructed. While I like the elegance
> and
> > > > > >    symmetry, I believe this will lead to substantially more work
> in
> > > > > moving
> > > > > >    from serialization format to something closer to what a system
> > would
> > > > > > want
> > > > > >    to manipulate/consume. The reality is that there are a lot of
> > really
> > > > > > known
> > > > > >    things and specializing the representation for these things
> will
> > > > > > ultimately
> > > > > >    make things easier to program with without error and easier to
> > > > debug.
> > > > > > (For
> > > > > >    example, imagine trying to inspect a plan in a debugging
> session
> > > > with
> > > > > > the
> > > > > >    Ben representation.) We should embrace the known things in the
> > > > > >    specification.
> > > > > >    - I believe that it is a mistake for the inner workings of the
> > plan
> > > > to
> > > > > >    ever use field names. Only input (e.g. file read) and Output
> > (e.g.
> > > > > > return
> > > > > >    to user or write to file) need to have field names. For the
> > rest of
> > > > > the
> > > > > >    system, using field ordinals (determinant whether nested or
> > flat) is
> > > > > > much
> > > > > >    cleaner and is how most execution systems work. For example,
> in
> > > > > Impala I
> > > > > >    believe it is called a slot. As I noted in the PR, Calcite as
> an
> > > > > > example is
> > > > > >    entirely ordinal based at the algebra level. Rowtypes contain
> > field
> > > > > > names
> > > > > >    but they are actually basically pointless. Field references
> use
> > > > > > RexInputRef
> > > > > >    with ordinal based and rules around column order output (e.g.
> > what
> > > > is
> > > > > > the
> > > > > >    field order of a join output) are determinant and done
> entirely
> > at
> > > > an
> > > > > >    ordinal level. The only place where names should be used
> > (besides
> > > > > >    input/output) is in the case of map keys. In that case, the
> > names
> > > > are
> > > > > >    actually data, as opposed to scheme metadata. This is why I
> > propose
> > > > a
> > > > > >    strongly structured dereference operation [1].
> > > > > >    - Properties should only be included in the serialization if
> > they
> > > > are
> > > > > >    not easily re-derivable at plan consumption time. For example,
> > > > you'll
> > > > > > note
> > > > > >    that I don't store schema information for relational
> operation.
> > Each
> > > > > >    function and relational operation should already know how a
> > given
> > > > > input
> > > > > > is
> > > > > >    transformed to a given output. Capturing this information in
> the
> > > > > > plan/IR is
> > > > > >    excessive. In many ways, I compare it to the early use of
> > > > VectorLayout
> > > > > > [2]
> > > > > >    in Arrow schema. It may have provided some additional checksum
> > of
> > > > the
> > > > > >    message but ultimately it caused more pain than it was worth
> > (and
> > > > thus
> > > > > > we
> > > > > >    removed it before formalizing the specification). For
> > reference, in
> > > > > the
> > > > > >    context of Dremio, we used to actually do this, send schema
> > > > > information
> > > > > >    around for all operations. We removed it because in many cases
> > > > > becoming
> > > > > > the
> > > > > >    majority of our internal plan serialization (imagine simple
> > > > operations
> > > > > > that
> > > > > >    are carrying 1000s of fields).
> > > > > >    - I suggest focusing on support for both logical and physical
> > > > > >    representations. The moment you start talking about
> optimization
> > > > > passes,
> > > > > >    many of those would probably be better being done at the
> logical
> > > > > level.
> > > > > > The
> > > > > >    overlap is really high.
> > > > > >    - I think a lot more work must be done before introducing UDFs
> > and
> > > > > user
> > > > > >    defined relational operations. I see one goal being the
> > possibility
> > > > of
> > > > > >    there being three systems: A -> B -> C. A is a IR producer. C
> > is a
> > > > IR
> > > > > >    consumer and B is a IR filter or translator. In this
> situation,
> > B
> > > > > > should be
> > > > > >    able to operate and do optimizations on a plan even if if
> there
> > are
> > > > > > black
> > > > > >    box user defined operations. Being able to know the
> > > > > > properties-preservation
> > > > > >    or not of these operations is important to making decisions.
> For
> > > > > > example,
> > > > > >    does a user defined relational operation maintain sortedness?
> > > > > > Distribution?
> > > > > >    Is a defined UDF idempotent? As such, I think the definition
> of
> > > > those
> > > > > > black
> > > > > >    boxes should be much more structured. For example: it is a
> > python
> > > > > >    relational operation named X stored in Y that maintains
> > properties
> > > > 1,2
> > > > > > and
> > > > > >    disrupts property 3. Putting just a black box of bytes will
> > > > > > substantially
> > > > > >    reduce the compatibility and extensibility of the ecosystem of
> > tools
> > > > > >    working against IR. I'd note that I wouldn't expect this to
> be a
> > > > > burden
> > > > > > to
> > > > > >    actual end users. By using sensible defaults, I still would
> > expect
> > > > an
> > > > > > end
> > > > > >    user tool to support arbitrary user defined operations.
> > > > > >    - It might make sense to review the XML representation that
> Orca
> > > > uses
> > > > > >    [3]. I haven't looked at it recently but they had a strong
> goal
> > of
> > > > > >    decoupling for most of its life (to use in both Greenplum and
> > Hawq).
> > > > > It
> > > > > >    could be the most mature/formal serialization of query plans
> > > > > publically
> > > > > >    available.
> > > > > >
> > > > > >
> > > > > > [1]
> > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://github.com/apache/arrow/pull/10979/files#diff-e40fbc40cf7a131efd2cb098444931774cfad046b8665b38452258ffaa2e3423R34
> > > > > > [2]
> > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://github.com/apache/arrow/commit/611a4b951e24f4f967c3d382a2027dc035fc37f0
> > > > > > [3] https://github.com/greenplum-db/gporca
> > > > > >
> > > > > >
> > > > > > On Tue, Aug 17, 2021 at 11:14 AM Phillip Cloud <
> cpcloud@gmail.com>
> > > > > wrote:
> > > > > >
> > > > > > > On Tue, Aug 17, 2021 at 10:56 AM Wes McKinney <
> > wesmckinn@gmail.com>
> > > > > > wrote:
> > > > > > >
> > > > > > > > Looking at Ben's alternate PR [1], having an IR that leans
> > heavily
> > > > on
> > > > > > > > memory references to an out-of-band data sidecar seems like
> an
> > > > > > > > approach that would substantially ratchet up the
> implementation
> > > > > > > > complexity as producing the IR would then have the level of
> > > > > complexity
> > > > > > > > of producing the Arrow IPC format — when producing the "root"
> > Plan
> > > > > > > > message, you must accumulate a list of the dependent
> serialized
> > > > > > > > submessages, placing the appropriate Buffer memory offset in
> > the
> > > > Plan
> > > > > > > > message, like we do when producing the RecordBatch.buffers
> > field.
> > > > > This
> > > > > > > > seems complicated to me as you must devise a custom binary
> > protocol
> > > > > to
> > > > > > > > concatenate the serialized Plan and the messages it depends
> on
> > > > into a
> > > > > > > > single binary payload
> > > > > > > >
> > > > > > > > <ROOT PLAN>
> > > > > > > > <padding>
> > > > > > > > <Buffer 0>
> > > > > > > > <padding>
> > > > > > > > <Buffer 1>
> > > > > > > > <padding>
> > > > > > > > ...
> > > > > > > > <Buffer N - 1>
> > > > > > > >
> > > > > > > > (one purpose of FlatBufferBuilder is to spare you having to
> do
> > this
> > > > > > > > yourself — some reasons we do it for the Arrow IPC format is
> > > > because
> > > > > > > > appending Arrow memory buffers directly to a
> FlatBufferBuilder
> > > > would
> > > > > > > > be inefficient — internal realloc calls — and Flatbuffers are
> > > > limited
> > > > > > > > to 2GB. Neither of these things are problems here)
> > > > > > > >
> > > > > > > > In general, I believe the output created by an IR producer
> > should
> > > > be
> > > > > a
> > > > > > > > single serialized object without any out-of-band data
> sidecar —
> > > > this
> > > > > > > > is much simpler for implementers and we can still provide an
> > > > "escape
> > > > > > > > hatch" for user-defined operators and functions where the
> > required
> > > > > > > > function/operator is passed opaquely as an embedded binary
> > data.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > The serialization format (whether it is Flatbuffers or JSON, or
> > > > > > > > something else) should allow for data memoization, so if
> there
> > is a
> > > > > > > > user-defined operator/function, or a relation that is used
> > multiple
> > > > > > > > times throughout the query (potentially with a large schema),
> > then
> > > > we
> > > > > > > > should ensure that the data need not be duplicated in the
> > > > > > > > serialization format unnecessarily — in Flatbuffers, you can
> > > > achieve
> > > > > > > > this by reusing offsets, but we could devise the data
> > structures to
> > > > > > > > make the memoization of "expensive" objects more explicit.
> > > > > > > >
> > > > > > >
> > > > > > > I think this is something that would need to be explicitly
> > encoded in
> > > > > > > the structures themselves if it's a hard requirement. I don't
> > think
> > > > > this
> > > > > > > should block
> > > > > > > a prototype producer/consumer.
> > > > > > >
> > > > > > > Is there something in the second PR/design that precludes the
> > reuse
> > > > of
> > > > > > > offsets?
> > > > > > > To my eye, the flatbuffers offset reuse mechanism works just as
> > well
> > > > > > there.
> > > > > > >
> > > > > > >
> > > > > > > > I additionally think that it is important to provide as much
> > > > built-in
> > > > > > > > support for "canonical" operators/functions (such as the ones
> > > > > > > > implemented commonly by SQL engines) as possible, and to
> > liberally
> > > > > > > > expand the catalogue of "built-in" capabilities. I would
> still
> > > > prefer
> > > > > > > > to have large unions/enums of built-in operators/functions
> and
> > to
> > > > > > > > expand those unions/enums to accommodate new things when it
> is
> > > > > > > > demonstrated that there is a need to standardize things
> between
> > > > > > > > producers/consumers.
> > > > > > > >
> > > > > > >
> > > > > > > I think there's a middle ground where we add a bit of structure
> > > > > > (something
> > > > > > > like
> > > > > > > a descriptor from the first PR) to indicate whether a thing is
> > > > built-in
> > > > > > vs
> > > > > > > user-defined.
> > > > > > > It looks like Ben has pushed something like this to his PR.
> > > > > > >
> > > > > > > With that scheme, we have both flexibility and a small set of
> > special
> > > > > > > builtins that make up
> > > > > > > a statically typed set for expressions and relational
> operators.
> > > > > > >
> > > > > > > I would really like to vet this PR with a prototype this week,
> > > > > > > to see whether we need to revisit any major choices. I don't
> > think
> > > > > we'll
> > > > > > be
> > > > > > > able to
> > > > > > > anticipate all the consequences until we write some code.
> > > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > One of the beneficial properties of the Union/Enum approach
> > for the
> > > > > > > > operator/function catalogues, is that when there are
> additions
> > to
> > > > > > > > those enums, the generated Flatbuffers files will cause many
> > > > language
> > > > > > > > compilers to warn or error on unhandled enum cases. If all
> > > > > > > > function/operator names are strings, then you are essentially
> > > > > > > > reimplementing the functionality provided by enums by hand. I
> > > > > > > > initially used strings for all function references in my
> > original
> > > > > > > > prototype, but I now think that using an enum for "built-ins"
> > would
> > > > > be
> > > > > > > > superior (because of the code-generated enum interface) and
> > not a
> > > > > > > > premature optimization.
> > > > > > > >
> > > > > > > > [1]: https://github.com/apache/arrow/pull/10934
> > > > > > > >
> > > > > > > > On Fri, Aug 13, 2021 at 11:26 PM Phillip Cloud <
> > cpcloud@gmail.com>
> > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > Hey all,
> > > > > > > > >
> > > > > > > > > Just wanted to give an update on the effort here.
> > > > > > > > >
> > > > > > > > > Ben Kietzman has created an alternative proposal to the
> > initial
> > > > > > design
> > > > > > > > [1].
> > > > > > > > > It largely overlaps with the original, but differs in a few
> > > > > important
> > > > > > > > ways:
> > > > > > > > >
> > > > > > > > > * A big focus of the design is on flexibility, allowing
> > > > producers,
> > > > > > > > > consumers and ultimately end users of those systems the
> > ability
> > > > to
> > > > > > > define
> > > > > > > > > custom operations in the graph.
> > > > > > > > > * There are very few predefined relational operations
> > (project,
> > > > > > filter,
> > > > > > > > > join and a handful of others).
> > > > > > > > > * There are only 3 types of value expressions: literals,
> > field
> > > > > > > > references,
> > > > > > > > > and function calls.
> > > > > > > > > * The model of evaluation is one that requires a final sink
> > node,
> > > > > to
> > > > > > > > > indicate where the record batches from child relations end
> > up (a
> > > > > > file,
> > > > > > > a
> > > > > > > > > socket, an in-memory buffer, etc).
> > > > > > > > >
> > > > > > > > > I've added notes [2] to the original Google doc (under the
> > > > > > Alternative
> > > > > > > > > Design Notes subheading), and a few pseudocode examples.
> > > > > > > > > Unfortunately, these went out of date as soon as Ben pushed
> > the
> > > > PR
> > > > > > [3],
> > > > > > > > so
> > > > > > > > > I need to update those to reflect his changes. Regardless,
> > > > > > > > > the design is broadly the same, so it should still give a
> > good
> > > > > > > indication
> > > > > > > > > of the details of the design.
> > > > > > > > >
> > > > > > > > > There are a decent number of review comments on the
> original
> > PR
> > > > > that
> > > > > > I
> > > > > > > > plan
> > > > > > > > > to port over where they are still relevant.
> > > > > > > > > I also plan on adding support for window functions either
> > tonight
> > > > > or
> > > > > > on
> > > > > > > > > Monday.
> > > > > > > > >
> > > > > > > > > Please review this design at your earliest convenience.
> Since
> > > > > > there's a
> > > > > > > > > fairly concrete set of types in flatbuffers that
> > > > > > > > > we can look at, ideally we can center discussion around the
> > > > details
> > > > > > in
> > > > > > > > the
> > > > > > > > > PR.
> > > > > > > > >
> > > > > > > > > Thanks!
> > > > > > > > >
> > > > > > > > > [1]: https://github.com/apache/arrow/pull/10856
> > > > > > > > > [2]:
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://docs.google.com/document/d/1C_XVOG7iFkl6cgWWMyzUoIjfKt-X2UxqagPJrla0bAE/edit#heading=h.4tfbbtaqzu13
> > > > > > > > > [3]: https://github.com/apache/arrow/pull/10934
> > > > > > > > >
> > > > > > > > > On Thu, Aug 12, 2021 at 3:55 PM Julian Hyde <
> > > > > jhyde.apache@gmail.com>
> > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > > > Wes wrote:
> > > > > > > > > > >
> > > > > > > > > > > Supporting this kind of intra-application engine
> > > > > > > > > > > heterogeneity is one of the motivations for the
> project.
> > > > > > > > > >
> > > > > > > > > > +1
> > > > > > > > > >
> > > > > > > > > > The data format is the natural interface between tasks.
> > > > (Defining
> > > > > > > > “task”
> > > > > > > > > > here as “something that is programmed using the IR”.)
> That
> > is
> > > > > > Arrow’s
> > > > > > > > > > strength.
> > > > > > > > > >
> > > > > > > > > > So I think the IR should describe what each task should
> > do, and
> > > > > > tasks
> > > > > > > > > > should be fairly small. Not whole relational operators,
> > > > operating
> > > > > > on
> > > > > > > > whole
> > > > > > > > > > tables, but pieces of relational operators, operating on
> > > > batches
> > > > > or
> > > > > > > > > > sequences of batches.
> > > > > > > > > >
> > > > > > > > > > Elsethread, someone mentioned the LoLePop concept and the
> > > > > > > > Kohn/Leis/Neuman
> > > > > > > > > > paper [1]. The LoLePop concept sounds good for our
> > purposes.
> > > > > > > > > >
> > > > > > > > > > Julian
> > > > > > > > > >
> > > > > > > > > > [1]
> > https://db.in.tum.de/~kohn/papers/lolepops-sigmod21.pdf
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > > On Aug 12, 2021, at 5:19 AM, Wes McKinney <
> > > > wesmckinn@gmail.com
> > > > > >
> > > > > > > > wrote:
> > > > > > > > > > >
> > > > > > > > > > > On Wed, Aug 11, 2021 at 11:22 PM Phillip Cloud <
> > > > > > cpcloud@gmail.com>
> > > > > > > > > > wrote:
> > > > > > > > > > >>
> > > > > > > > > > >> On Wed, Aug 11, 2021 at 4:48 PM Jorge Cardoso Leitão <
> > > > > > > > > > >> jorgecarleitao@gmail.com> wrote:
> > > > > > > > > > >>
> > > > > > > > > > >>> Couple of questions
> > > > > > > > > > >>>
> > > > > > > > > > >>> 1. Is the goal that IRs have equal semantics, i.e.
> > given
> > > > > > > > (IR,data), the
> > > > > > > > > > >>> operation "(IR,data) - engine -> result" MUST be the
> > same
> > > > for
> > > > > > all
> > > > > > > > > > "engine"?
> > > > > > > > > > >>>
> > > > > > > > > > >>
> > > > > > > > > > >> I think that might be a non-starter for mundane
> reasons:
> > > > > there's
> > > > > > > > > > probably
> > > > > > > > > > >> at least two engines
> > > > > > > > > > >> that disagree on the result of sum(x) where x is a
> > floating
> > > > > > point
> > > > > > > > > > column.
> > > > > > > > > > >>
> > > > > > > > > > >>
> > > > > > > > > > >>> 2. if yes, imo we may need to worry about:
> > > > > > > > > > >>> * a definition of equality that implementations agree
> > on.
> > > > > > > > > > >>> * agreement over what the semantics look like. For
> > example,
> > > > > do
> > > > > > we
> > > > > > > > use
> > > > > > > > > > >>> kleene logic for AND and OR?
> > > > > > > > > > >>>
> > > > > > > > > > >>
> > > > > > > > > > >> WRT Kleene logic my thoughts are that the IR should
> > support
> > > > > both
> > > > > > > > Kleene
> > > > > > > > > > and
> > > > > > > > > > >> non-Kleene,
> > > > > > > > > > >> and producers can choose their desired semantics.
> > > > > > > > > > >>
> > > > > > > > > > >> Ibis for example, would override the `&` operator in
> `a
> > & b`
> > > > > to
> > > > > > > > produce
> > > > > > > > > > >> `KleeneAnd(Column(a), Column(b))`.
> > > > > > > > > > >>
> > > > > > > > > > >>
> > > > > > > > > > >>>
> > > > > > > > > > >>> To try to understand the gist, let's pick an
> aggregated
> > > > count
> > > > > > > over
> > > > > > > > a
> > > > > > > > > > >>> column: engines often do partial counts over
> partitions
> > > > > > followed
> > > > > > > > by a
> > > > > > > > > > final
> > > > > > > > > > >>> "sum" over the partial counts. Is the idea that the
> > query
> > > > > > engine
> > > > > > > > would
> > > > > > > > > > >>> communicate with the compute engine via 2 IRs where
> > one is
> > > > > > "count
> > > > > > > > me
> > > > > > > > > > these"
> > > > > > > > > > >>> the other is "sum me these"?
> > > > > > > > > > >>>
> > > > > > > > > > >>> Best,
> > > > > > > > > > >>> Jorge
> > > > > > > > > > >>>
> > > > > > > > > > >>
> > > > > > > > > > >> Not in its current incarnation.
> > > > > > > > > > >>
> > > > > > > > > > >> The idea is that the IR producer communicates a desire
> > to
> > > > > > count(x)
> > > > > > > > to a
> > > > > > > > > > >> consumer, and  it's up to the consumer to figure out
> > how to
> > > > > turn
> > > > > > > > that
> > > > > > > > > > count
> > > > > > > > > > >> into something that makes sense for itself. In your
> > example
> > > > > > > that's a
> > > > > > > > > > series
> > > > > > > > > > >> of partial counts followed by a sum.
> > > > > > > > > > >>
> > > > > > > > > > >
> > > > > > > > > > > That said, I think there is a valid use case here
> where a
> > > > > system
> > > > > > > > might
> > > > > > > > > > > make use of different engines to execute different
> > > > (composable)
> > > > > > > > layers
> > > > > > > > > > > of a complex query.
> > > > > > > > > > >
> > > > > > > > > > > For example:
> > > > > > > > > > >
> > > > > > > > > > > * suppose you want to scan and do predicate pushdown on
> > an
> > > > > > unusual
> > > > > > > > > > > data source that is only accessible from one particular
> > > > engine
> > > > > > but
> > > > > > > > > > > * you need to do some analytical operation with the
> scan
> > > > > results
> > > > > > > that
> > > > > > > > > > > is only supported by another engine
> > > > > > > > > > >
> > > > > > > > > > > You could decompose the query into two stages with an
> IR
> > > > > > relational
> > > > > > > > > > > expression for each stage and use then the engines
> > together
> > > > to
> > > > > > > > > > > accomplish what you need (of course, you would need an
> > > > > > > orchestration
> > > > > > > > > > > layer to handle plumbing the query engine inputs and
> > outputs
> > > > > > > together
> > > > > > > > > > > as Arrow streams). Supporting this kind of
> > intra-application
> > > > > > engine
> > > > > > > > > > > heterogeneity is one of the motivations for the
> project.
> > > > > > > > > > >
> > > > > > > > > > >>>
> > > > > > > > > > >>>
> > > > > > > > > > >>>
> > > > > > > > > > >>>
> > > > > > > > > > >>>
> > > > > > > > > > >>> On Wed, Aug 11, 2021 at 6:10 PM Phillip Cloud <
> > > > > > cpcloud@gmail.com
> > > > > > > >
> > > > > > > > > > wrote:
> > > > > > > > > > >>>
> > > > > > > > > > >>>> Thanks Wes,
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Great to be back working on Arrow again and engaging
> > with
> > > > > the
> > > > > > > > > > community.
> > > > > > > > > > >>> I
> > > > > > > > > > >>>> am really excited about this effort.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> I think there are a number of concerns I see as
> > important
> > > > to
> > > > > > > > address
> > > > > > > > > > in
> > > > > > > > > > >>> the
> > > > > > > > > > >>>> compute IR proposal:
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 1. Requirement for output types.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> I think that so far there's been many reasons for
> > > > requiring
> > > > > > > > > > conforming IR
> > > > > > > > > > >>>> producers and consumers to adhere to output types,
> > but I
> > > > > > haven't
> > > > > > > > seen
> > > > > > > > > > a
> > > > > > > > > > >>>> strong rationale for keeping them optional (in the
> > > > semantic
> > > > > > > > sense, not
> > > > > > > > > > >>> WRT
> > > > > > > > > > >>>> any particular serialization format's representation
> > of
> > > > > > > > optionality).
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> I think a design that includes unambiguous semantics
> > for
> > > > > > output
> > > > > > > > types
> > > > > > > > > > (a
> > > > > > > > > > >>>> consumer must produce a value of the requested type
> or
> > > > it's
> > > > > an
> > > > > > > > > > >>>> error/non-conforming) is simpler to reason about for
> > > > > > producers,
> > > > > > > > and
> > > > > > > > > > >>>> provides a strong guarantee for end users (humans or
> > > > > machines
> > > > > > > > > > >>> constructing
> > > > > > > > > > >>>> IR from an API and expecting the thing they ask for
> > back
> > > > > from
> > > > > > > the
> > > > > > > > IR
> > > > > > > > > > >>>> consumer).
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 2. Flexibility
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> The current PR is currently unable to support what I
> > think
> > > > > are
> > > > > > > > killer
> > > > > > > > > > >>>> features of the IR: custom operators (relational or
> > > > column)
> > > > > > and
> > > > > > > > UDFs.
> > > > > > > > > > In
> > > > > > > > > > >>> my
> > > > > > > > > > >>>> mind, on top of the generalized compute description
> > that
> > > > the
> > > > > > IR
> > > > > > > > > > offers,
> > > > > > > > > > >>> the
> > > > > > > > > > >>>> ability for producers and consumers of IR to extend
> > the IR
> > > > > > > without
> > > > > > > > > > >>> needing
> > > > > > > > > > >>>> to modify Arrow or depend on anything except the
> > format is
> > > > > > > itself
> > > > > > > > > > >>> something
> > > > > > > > > > >>>> that is necessary to gain adoption.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Developers will need to build custom relational
> > operators
> > > > > > (e.g.,
> > > > > > > > > > scans of
> > > > > > > > > > >>>> backends that don't exist anywhere for which a user
> > has
> > > > code
> > > > > > to
> > > > > > > > > > >>> implement)
> > > > > > > > > > >>>> and custom functions (anything operating on a column
> > that
> > > > > > > doesn't
> > > > > > > > > > already
> > > > > > > > > > >>>> exist, really). Furthermore, I think we can actually
> > drive
> > > > > > > > building an
> > > > > > > > > > >>>> Arrow consumer using the same API that an end user
> > would
> > > > use
> > > > > > to
> > > > > > > > extend
> > > > > > > > > > >>> the
> > > > > > > > > > >>>> IR.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 3. Window Functions
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Window functions are, I think, an important part of
> > the IR
> > > > > > value
> > > > > > > > > > >>>> proposition, as they are one of the more complex
> > operators
> > > > > in
> > > > > > > > > > databases.
> > > > > > > > > > >>> I
> > > > > > > > > > >>>> think we need to have something in the initial IR
> > proposal
> > > > > to
> > > > > > > > support
> > > > > > > > > > >>> these
> > > > > > > > > > >>>> operations.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 4. Non relational Joins
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Things like as-of join and window join operators
> > aren't
> > > > yet
> > > > > > > > fleshed
> > > > > > > > > > out
> > > > > > > > > > >>> in
> > > > > > > > > > >>>> the IR, and I'm not sure they should be in scope for
> > the
> > > > > > initial
> > > > > > > > > > >>> prototype.
> > > > > > > > > > >>>> I think once we settle on a design, we can work the
> > design
> > > > > of
> > > > > > > > these
> > > > > > > > > > >>>> particular operators out during the initial
> > prototype. I
> > > > > think
> > > > > > > the
> > > > > > > > > > >>>> specification of these operators should basically be
> > PR #2
> > > > > > after
> > > > > > > > the
> > > > > > > > > > >>>> initial design lands.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> # Order of Work
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 1. Nail down the design. Anything else is a
> > non-starter.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 2. Prototype an IR producer using Ibis
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Ibis is IMO a good candidate for a first IR producer
> > as it
> > > > > > has a
> > > > > > > > > > number
> > > > > > > > > > >>> of
> > > > > > > > > > >>>> desirable properties that make prototyping faster
> and
> > > > allow
> > > > > > for
> > > > > > > > us to
> > > > > > > > > > >>>> refine the design of the IR as needed based on how
> the
> > > > > > > > implementation
> > > > > > > > > > >>> goes:
> > > > > > > > > > >>>> * It's written in Python so it has native support
> for
> > > > nearly
> > > > > > all
> > > > > > > > of
> > > > > > > > > > >>>> flatbuffers' features without having to creating
> > bindings
> > > > to
> > > > > > > C++.
> > > > > > > > > > >>>> * There's already a set of rules for type checking,
> as
> > > > well
> > > > > as
> > > > > > > > APIs
> > > > > > > > > > for
> > > > > > > > > > >>>> constructing expression trees, which means we don't
> > need
> > > > to
> > > > > > > worry
> > > > > > > > > > about
> > > > > > > > > > >>>> building a type checker for the prototype.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 3. Prototype an IR consumer in C++
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> I think in parallel to the producer prototype we can
> > > > further
> > > > > > > > inform
> > > > > > > > > > the
> > > > > > > > > > >>>> design from the consumer side by prototyping an IR
> > > > consumer
> > > > > in
> > > > > > > > C++ . I
> > > > > > > > > > >>> know
> > > > > > > > > > >>>> Ben Kietzman has expressed interest in working on
> > this.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Very interested to hear others' thoughts.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> -Phillip
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> On Tue, Aug 10, 2021 at 10:56 AM Wes McKinney <
> > > > > > > > wesmckinn@gmail.com>
> > > > > > > > > > >>> wrote:
> > > > > > > > > > >>>>
> > > > > > > > > > >>>>> Thank you for all the feedback and comments on the
> > > > > document.
> > > > > > > I'm
> > > > > > > > on
> > > > > > > > > > >>>>> vacation this week, so I'm delayed responding to
> > > > > everything,
> > > > > > > but
> > > > > > > > I
> > > > > > > > > > >>>>> will get to it as quickly as I can. I will be at
> > VLDB in
> > > > > > > > Copenhagen
> > > > > > > > > > >>>>> next week if anyone would like to chat in person
> > about
> > > > it,
> > > > > > and
> > > > > > > > we can
> > > > > > > > > > >>>>> relay the content of any discussions back to the
> > > > > > > > document/PR/e-mail
> > > > > > > > > > >>>>> thread.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> I know that Phillip Cloud expressed interest in
> > working
> > > > on
> > > > > > the
> > > > > > > > PR and
> > > > > > > > > > >>>>> helping work through many of the details, so I'm
> > glad to
> > > > > have
> > > > > > > the
> > > > > > > > > > >>>>> help. If there are others who would like to work on
> > the
> > > > PR
> > > > > or
> > > > > > > dig
> > > > > > > > > > into
> > > > > > > > > > >>>>> the details, please let me know. We might need to
> > figure
> > > > > out
> > > > > > > how
> > > > > > > > to
> > > > > > > > > > >>>>> accommodate "many cooks" by setting up the
> ComputeIR
> > > > > project
> > > > > > > > > > somewhere
> > > > > > > > > > >>>>> separate from the format/ directory to permit it to
> > exist
> > > > > in
> > > > > > a
> > > > > > > > > > >>>>> Work-In-Progress status for a period of time until
> we
> > > > work
> > > > > > > > through
> > > > > > > > > > the
> > > > > > > > > > >>>>> various details and design concerns.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> Re Julian's comment
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>>> The biggest surprise is that this language does
> full
> > > > > > > relational
> > > > > > > > > > >>>>> operations. I was expecting that it would do
> > fragments of
> > > > > the
> > > > > > > > > > >>> operations.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> There's a related but different (yet still
> > interesting
> > > > and
> > > > > > > > worthy of
> > > > > > > > > > >>>>> analysis) problem of creating an "engine language"
> > that
> > > > > > > describes
> > > > > > > > > > more
> > > > > > > > > > >>>>> mechanically the constituent parts of implementing
> > the
> > > > > > > relational
> > > > > > > > > > >>>>> operators. To create a functional computation
> > language
> > > > with
> > > > > > > > concrete
> > > > > > > > > > >>>>> Arrow data structures as a top-level primitive
> sounds
> > > > like
> > > > > an
> > > > > > > > > > >>>>> interesting research area where I could see
> something
> > > > > > > developing
> > > > > > > > > > >>>>> eventually.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> The main problem I'm interested in solving right
> now
> > is
> > > > > > > enabling
> > > > > > > > > > front
> > > > > > > > > > >>>>> ends that have sufficient understanding of
> relational
> > > > > algebra
> > > > > > > and
> > > > > > > > > > data
> > > > > > > > > > >>>>> frame operations to talk to engines without having
> > to go
> > > > > > > > backwards
> > > > > > > > > > >>>>> from their logical query plans to SQL. So as
> > mentioned in
> > > > > the
> > > > > > > > > > >>>>> document, being able to faithfully carry the
> > relational
> > > > > > > operator
> > > > > > > > node
> > > > > > > > > > >>>>> information generated by Calcite or Ibis or another
> > > > system
> > > > > > > would
> > > > > > > > be
> > > > > > > > > > >>>>> super useful. Defining the semantics of various
> > kinds of
> > > > > > > > user-defined
> > > > > > > > > > >>>>> functions would also be helpful to standardize the
> > > > > > > > > > >>>>> engine-to-user-language UDF/extension interface.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> On Tue, Aug 10, 2021 at 2:36 PM Dimitri Vorona <
> > > > > > > > alendit@gmail.com>
> > > > > > > > > > >>>> wrote:
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> Hi Wes,
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> cool initiative! Reminded me of "Building Advanced
> > SQL
> > > > > > > Analytics
> > > > > > > > > > From
> > > > > > > > > > >>>>>> Low-Level Plan Operators" from SIGMOD 2021 (
> > > > > > > > > > >>>>>>
> > http://db.in.tum.de/~kohn/papers/lolepops-sigmod21.pdf)
> > > > > > which
> > > > > > > > > > >>>> proposes a
> > > > > > > > > > >>>>>> set of building block for advanced aggregation.
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> Cheers,
> > > > > > > > > > >>>>>> Dimitri.
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> On Thu, Aug 5, 2021 at 7:59 PM Julian Hyde <
> > > > > > > > jhyde.apache@gmail.com>
> > > > > > > > > > >>>>> wrote:
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>>> Wes,
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>> Thanks for this. I’ve added comments to the doc
> > and to
> > > > > the
> > > > > > > PR.
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>> The biggest surprise is that this language does
> > full
> > > > > > > relational
> > > > > > > > > > >>>>>>> operations. I was expecting that it would do
> > fragments
> > > > of
> > > > > > the
> > > > > > > > > > >>>>> operations.
> > > > > > > > > > >>>>>>> Consider join. A distributed hybrid hash join
> > needs to
> > > > > > > > partition
> > > > > > > > > > >>> rows
> > > > > > > > > > >>>>> into
> > > > > > > > > > >>>>>>> output buffers based on a hash key, build hash
> > tables,
> > > > > > probe
> > > > > > > > into
> > > > > > > > > > >>>> hash
> > > > > > > > > > >>>>>>> tables, scan hash tables for untouched
> > “outer”rows, and
> > > > > so
> > > > > > > > forth.
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>> I see Arrow’s compute as delivering each of those
> > > > > > operations,
> > > > > > > > > > >>> working
> > > > > > > > > > >>>>> on
> > > > > > > > > > >>>>>>> perhaps a batch at a time, or a sequence of
> > batches,
> > > > with
> > > > > > > some
> > > > > > > > > > >>> other
> > > > > > > > > > >>>>> system
> > > > > > > > > > >>>>>>> coordinating those tasks. So I would expect to
> see
> > > > > Arrow’s
> > > > > > > > compute
> > > > > > > > > > >>>>> language
> > > > > > > > > > >>>>>>> mainly operating on batches rather than a table
> > > > > > abstraction.
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>> Julian
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>>> On Aug 2, 2021, at 5:16 PM, Wes McKinney <
> > > > > > > wesmckinn@gmail.com
> > > > > > > > >
> > > > > > > > > > >>>>> wrote:
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> hi folks,
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> This idea came up in passing in the past --
> given
> > that
> > > > > > there
> > > > > > > > are
> > > > > > > > > > >>>>>>>> multiple independent efforts to develop
> > Arrow-native
> > > > > query
> > > > > > > > > > >>> engines
> > > > > > > > > > >>>>>>>> (and surely many more to come), it seems like it
> > would
> > > > > be
> > > > > > > > > > >>> valuable
> > > > > > > > > > >>>> to
> > > > > > > > > > >>>>>>>> have a way to enable user languages (like Java,
> > > > Python,
> > > > > R,
> > > > > > > or
> > > > > > > > > > >>> Rust,
> > > > > > > > > > >>>>>>>> for example) to communicate with backend
> computing
> > > > > engines
> > > > > > > > (like
> > > > > > > > > > >>>>>>>> DataFusion, or new computing capabilities being
> > built
> > > > in
> > > > > > the
> > > > > > > > > > >>> Arrow
> > > > > > > > > > >>>>> C++
> > > > > > > > > > >>>>>>>> library) in a fashion that is "lower-level" than
> > SQL
> > > > and
> > > > > > > > > > >>>> specialized
> > > > > > > > > > >>>>>>>> to Arrow's type system. So rather than leaving
> it
> > to a
> > > > > SQL
> > > > > > > > > > >>> parser /
> > > > > > > > > > >>>>>>>> analyzer framework to generate an expression
> tree
> > of
> > > > > > > > relational
> > > > > > > > > > >>>>>>>> operators and then translate that to an
> > Arrow-native
> > > > > > > > > > >>>> compute-engine's
> > > > > > > > > > >>>>>>>> internal grammer, a user framework could provide
> > the
> > > > > > desired
> > > > > > > > > > >>>>>>>> Arrow-native expression tree / data
> manipulations
> > > > > directly
> > > > > > > and
> > > > > > > > > > >>> skip
> > > > > > > > > > >>>>>>>> the SQL altogether.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> The idea of creating a "serialized intermediate
> > > > > > > representation
> > > > > > > > > > >>>> (IR)"
> > > > > > > > > > >>>>>>>> for Arrow compute operations would be to serve
> use
> > > > cases
> > > > > > > large
> > > > > > > > > > >>> and
> > > > > > > > > > >>>>>>>> small -- from the most complex TPC-* or time
> > series
> > > > > > database
> > > > > > > > > > >>> query
> > > > > > > > > > >>>> to
> > > > > > > > > > >>>>>>>> the most simple array predicate/filter sent with
> > an
> > > > RPC
> > > > > > > > request
> > > > > > > > > > >>>> using
> > > > > > > > > > >>>>>>>> Arrow Flight. It is deliberately language- and
> > > > > > > > engine-agnostic,
> > > > > > > > > > >>>> with
> > > > > > > > > > >>>>>>>> the only commonality across usages being the
> Arrow
> > > > > > columnar
> > > > > > > > > > >>> format
> > > > > > > > > > >>>>>>>> (schemas and array types). This would be better
> > than
> > > > > > leaving
> > > > > > > > it
> > > > > > > > > > >>> to
> > > > > > > > > > >>>>>>>> each application to develop its own bespoke
> > expression
> > > > > > > > > > >>>>> representations
> > > > > > > > > > >>>>>>>> for its needs.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> I spent a while thinking about this and wrote
> up a
> > > > brain
> > > > > > > dump
> > > > > > > > RFC
> > > > > > > > > > >>>>>>>> document [1] and accompanying pull request [2]
> > that
> > > > > makes
> > > > > > > the
> > > > > > > > > > >>>>> possibly
> > > > > > > > > > >>>>>>>> controversial choice of using Flatbuffers to
> > represent
> > > > > the
> > > > > > > > > > >>>> serialized
> > > > > > > > > > >>>>>>>> IR. I discuss the rationale for the choice of
> > > > > Flatbuffers
> > > > > > in
> > > > > > > > the
> > > > > > > > > > >>>> RFC
> > > > > > > > > > >>>>>>>> document. This PR is obviously deficient in many
> > > > regards
> > > > > > > > > > >>>> (incomplete,
> > > > > > > > > > >>>>>>>> hacky, or unclear in places), and will need some
> > help
> > > > > from
> > > > > > > > others
> > > > > > > > > > >>>> to
> > > > > > > > > > >>>>>>>> flesh out. I suspect that actually implementing
> > the IR
> > > > > > will
> > > > > > > be
> > > > > > > > > > >>>>>>>> necessary to work out many of the low-level
> > details.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> Note that this IR is intended to be more of a
> > > > "superset"
> > > > > > > > project
> > > > > > > > > > >>>> than
> > > > > > > > > > >>>>>>>> a "lowest common denominator". So there may be
> > things
> > > > > that
> > > > > > > it
> > > > > > > > > > >>>>> includes
> > > > > > > > > > >>>>>>>> which are only available in some engines (e.g.
> > engines
> > > > > > that
> > > > > > > > have
> > > > > > > > > > >>>>>>>> specialized handling of time series data).
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> As some of my personal motivation for the
> project,
> > > > > > > concurrent
> > > > > > > > > > >>> with
> > > > > > > > > > >>>>> the
> > > > > > > > > > >>>>>>>> genesis of Apache Arrow, I started a Python
> > project
> > > > > called
> > > > > > > > Ibis
> > > > > > > > > > >>> [3]
> > > > > > > > > > >>>>>>>> (which is similar to R's dplyr project) which
> > serves
> > > > as
> > > > > a
> > > > > > > > "Python
> > > > > > > > > > >>>>>>>> analytical query IR builder" that is capable of
> > > > > generating
> > > > > > > > most
> > > > > > > > > > >>> of
> > > > > > > > > > >>>>> the
> > > > > > > > > > >>>>>>>> SQL standard, targeting many different SQL
> > dialects
> > > > and
> > > > > > > other
> > > > > > > > > > >>>>> backends
> > > > > > > > > > >>>>>>>> (like pandas). Microsoft ([4]) and Google ([5])
> > have
> > > > > used
> > > > > > > this
> > > > > > > > > > >>>>> library
> > > > > > > > > > >>>>>>>> as a "many-SQL" middleware. As such, I would
> like
> > to
> > > > be
> > > > > > able
> > > > > > > > to
> > > > > > > > > > >>>>>>>> translate between the in-memory "logical query"
> > data
> > > > > > > > structures
> > > > > > > > > > >>> in
> > > > > > > > > > >>>> a
> > > > > > > > > > >>>>>>>> library like Ibis to a serialized format that
> can
> > be
> > > > > > > executed
> > > > > > > > by
> > > > > > > > > > >>>> many
> > > > > > > > > > >>>>>>>> different Arrow-native query engines. The
> > expression
> > > > > > > > primitives
> > > > > > > > > > >>>>>>>> available in Ibis should serve as helpful test
> > cases,
> > > > > too.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> I look forward to the community's comments on
> the
> > RFC
> > > > > > > document
> > > > > > > > > > >>> [1]
> > > > > > > > > > >>>>> and
> > > > > > > > > > >>>>>>>> pull request [2] -- I realize that arriving at
> > > > consensus
> > > > > > on
> > > > > > > a
> > > > > > > > > > >>>> complex
> > > > > > > > > > >>>>>>>> and ambitious project like this can be
> > challenging so
> > > > I
> > > > > > > > recommend
> > > > > > > > > > >>>>>>>> spending time on the "non-goals" section in the
> > RFC
> > > > and
> > > > > > ask
> > > > > > > > > > >>>> questions
> > > > > > > > > > >>>>>>>> if you are unclear about the scope of what
> > problems
> > > > this
> > > > > > is
> > > > > > > > > > >>> trying
> > > > > > > > > > >>>> to
> > > > > > > > > > >>>>>>>> solve. I would be happy to give Edit access on
> > the RFC
> > > > > > > > document
> > > > > > > > > > >>> to
> > > > > > > > > > >>>>>>>> others and would consider ideas about how to
> move
> > > > > forward
> > > > > > > with
> > > > > > > > > > >>>>>>>> something that is able to be implemented by
> > different
> > > > > > Arrow
> > > > > > > > > > >>>> libraries
> > > > > > > > > > >>>>>>>> in the reasonably near future.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> Thanks,
> > > > > > > > > > >>>>>>>> Wes
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> [1]:
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>
> > > > > > > > > > >>>
> > > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://docs.google.com/document/d/1C_XVOG7iFkl6cgWWMyzUoIjfKt-X2UxqagPJrla0bAE/edit#
> > > > > > > > > > >>>>>>>> [2]: https://github.com/apache/arrow/pull/10856
> > > > > > > > > > >>>>>>>> [3]: https://ibis-project.org/
> > > > > > > > > > >>>>>>>> [4]:
> > > > > > http://cidrdb.org/cidr2021/papers/cidr2021_paper08.pdf
> > > > > > > > > > >>>>>>>> [5]:
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>
> > > > > > > > > > >>>
> > > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://cloud.google.com/blog/products/databases/automate-data-validation-with-dvt
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>
> > > > > > > > > > >>>
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> >
>

Re: [DISCUSS] Developing an "Arrow Compute IR [Intermediate Representation]" to decouple language front ends from Arrow-native compute engines

[Jacques Nadeau <ja...@apache.org>]

As Phillip mentioned, I think there is something powerful in producing a
standard serialized representation of compute operations beyond just Arrow
and I'd really like to create a broader community around it. This has been
something I had been independently thinking about for the last several
months. The discussion here has inspired me to start making real progress
on this work. As such, I created a new repository and site where I've
started to put together work around a new specification for compute. I
would love for the people here to help define this and will be looking to a
number of other communities to also contribute. One of my goals has been to
break the specification into a number of much smaller pieces [1] so that we
can make progress on each subsection without being overwhelmed by the
amount of content that must be reviewed.

Would love to hear people's ideas on this initiative.

The site is here: https://substrait.io/
The repo is here: https://github.com/substrait-io/substrait

[1] https://substrait.io/spec/specification/#components



On Wed, Sep 1, 2021 at 3:26 PM Phillip Cloud <cp...@gmail.com> wrote:

> Hey everyone,
>
> As many of you know, the compute IR project has a lot of interested parties
> and has generated a lot of feedback. In light of some of the feedback we’ve
> received, we want to stress that the specification is intended to have
> input from many diverse points of view and that we welcome folks outside of
> the Arrow community. We think there’s immense potential for a compute IR
> that multiple projects--including those outside of the Arrow umbrella--can
> leverage.
>
> With that in mind, Jacques has been working on something outside of the
> Arrow repo that’ll be shared in a few days, that is designed to bring those
> viewpoints to bear on the problem of generic relational computation that
> lives outside of the Arrow project.
>
> Inside Arrow, we think that a version of the in-development IR
> specifications from the last several weeks will add a ton of value by
> informing this new effort and would like to continue to move forward with a
> work-in-progress IR inside of Arrow for the time being to enable some work
> on API development (independent of exactly how things are serialized) to
> take place. It is very likely that we will adopt this broader specification
> once the dust has settled, so the format inside of Arrow will be relatively
> unstable for a while and not have backwards compatibility guarantees for
> now.
>
> The primary focus of the Arrow IR will be on shoring up APIs (producers and
> consumers), and we will also be moving the compute IR flatbuffers files out
> the format directory into another top-level directory in the repo.
>
> Thanks,
> Phillip
>
> On Mon, Aug 30, 2021 at 7:30 PM Weston Pace <we...@gmail.com> wrote:
>
> > My (incredibly naive) interpretation is that there are three problems to
> > tackle.
> >
> > 1) How do you represent a graph and relational operators (join, union,
> > groupby, etc.)
> >  - The PR appears to be addressing this question fairly well
> > 2) How does a frontend query a backend to know what UDFs are supported.
> >  - I don't see anything in the spec for this (some comments touch on
> > it) but it seems like it would be necessary to build any kind of
> > system.
> > 3) Is there some well defined set of canonical UDFs that we can all
> > agree on the semantics for (e.g. addition, subtraction, etc.)
> >  - I thought, from earlier comments in this email thread, that the
> > goal was to avoid addressing this.  Although I think there is strong
> > value here as well.
> >
> > So what is the scope of this initiative?  If it is just #1 for example
> > then I don't see any need to put types in the IR (and I've commented
> > as such in the PR).  From a relational perspective isn't a UDF just a
> > black box Table -> UDF -> Table?
> >
> > On Mon, Aug 30, 2021 at 11:10 AM Phillip Cloud <cp...@gmail.com>
> wrote:
> > >
> > > Hey everyone,
> > >
> > > There's some interesting discussion around types and where their
> location
> > > is in the current PR [1] (and in fact whether to store them at all).
> > >
> > > It would be great to get some community feedback on this [2] part of
> the
> > PR
> > > in particular, because the choice of whether to store types at all has
> > > important design consequences.
> > >
> > > [1]: https://github.com/apache/arrow/pull/10934
> > > [2]: https://github.com/apache/arrow/pull/10934/files#r697025313
> > >
> > > On Fri, Aug 27, 2021 at 2:11 AM Micah Kornfield <emkornfield@gmail.com
> >
> > > wrote:
> > >
> > > > As an FYI, Iceberg is also considering an IR in relation to view
> > support
> > > > [1].  I chimed in and pointed them to this thread and Wes's doc.
> > Phillip
> > > > and Jacques chimed in there as well.
> > > >
> > > > [1]
> > > >
> > > >
> >
> https://mail-archives.apache.org/mod_mbox/iceberg-dev/202108.mbox/%3CCAKRVfm6h6WxQtp5fj8Yj8XWR1wFe8VohOkPuoZZGK-UHPhtwjQ%40mail.gmail.com%3E
> > > >
> > > > On Thu, Aug 26, 2021 at 12:40 PM Phillip Cloud <cp...@gmail.com>
> > wrote:
> > > >
> > > > > Thanks for the feedback Jacques, very helpful. In the latest
> version
> > of
> > > > the
> > > > > PR, I've tried to incorporate nearly all of these points.
> > > > >
> > > > > - I've incorporated most of what you had for dereferencing
> operations
> > > > into
> > > > > the PR, and gotten rid of schemas except on Read/Write relations.
> > > > > - With respect to properties, I've made a bunch more specific
> > operators,
> > > > > and kept user-defined things special case-y.
> > > > > - I haven't incorporated anything close to physical-plan things,
> but
> > I
> > > > > think that's a good follow up PR. Having separate representations
> for
> > > > > logical/physical plans seems like a waste of effort ultimately. I
> > think
> > > > we
> > > > > can find a good balance.
> > > > > - Agree on UDF support, I think that will have to evolve as the
> rest
> > of
> > > > the
> > > > > spec evolves. UDFs will need language-dedicated effort given the
> > large
> > > > > variety of languages that folks will want to use to define
> functions.
> > > > >
> > > > > On a separate note, in an effort to move this project forward I'd
> > like to
> > > > > do one final round of code review from anyone interested and then
> > merge
> > > > the
> > > > > PR after that.
> > > > > This spec will be unstable for a while, until we can work out all
> the
> > > > > design kinks and edge cases, and I think getting this initial spec
> > in is
> > > > > important to start that process.
> > > > >
> > > > >
> > > > > On Mon, Aug 23, 2021 at 1:53 PM Jacques Nadeau <jacques@apache.org
> >
> > > > wrote:
> > > > >
> > > > > > In a lucky turn of events, Phillip actually turned out to be in
> my
> > neck
> > > > > of
> > > > > > the woods on Friday so we had a chance to sit down and discuss
> > this. To
> > > > > > help, I actually shared something I had been working on a few
> > months
> > > > ago
> > > > > > independently (before this discussion started).
> > > > > >
> > > > > > For reference:
> > > > > > Wes PR: https://github.com/apache/arrow/pull/10856
> > > > > > Ben PR: https://github.com/apache/arrow/pull/10934
> > > > > > Jacques PR: https://github.com/apache/arrow/pull/10979
> > > > > >
> > > > > > The high level points of feedback I have are:
> > > > > >
> > > > > >    - Ben PR feels too deconstructed. While I like the elegance
> and
> > > > > >    symmetry, I believe this will lead to substantially more work
> in
> > > > > moving
> > > > > >    from serialization format to something closer to what a system
> > would
> > > > > > want
> > > > > >    to manipulate/consume. The reality is that there are a lot of
> > really
> > > > > > known
> > > > > >    things and specializing the representation for these things
> will
> > > > > > ultimately
> > > > > >    make things easier to program with without error and easier to
> > > > debug.
> > > > > > (For
> > > > > >    example, imagine trying to inspect a plan in a debugging
> session
> > > > with
> > > > > > the
> > > > > >    Ben representation.) We should embrace the known things in the
> > > > > >    specification.
> > > > > >    - I believe that it is a mistake for the inner workings of the
> > plan
> > > > to
> > > > > >    ever use field names. Only input (e.g. file read) and Output
> > (e.g.
> > > > > > return
> > > > > >    to user or write to file) need to have field names. For the
> > rest of
> > > > > the
> > > > > >    system, using field ordinals (determinant whether nested or
> > flat) is
> > > > > > much
> > > > > >    cleaner and is how most execution systems work. For example,
> in
> > > > > Impala I
> > > > > >    believe it is called a slot. As I noted in the PR, Calcite as
> an
> > > > > > example is
> > > > > >    entirely ordinal based at the algebra level. Rowtypes contain
> > field
> > > > > > names
> > > > > >    but they are actually basically pointless. Field references
> use
> > > > > > RexInputRef
> > > > > >    with ordinal based and rules around column order output (e.g.
> > what
> > > > is
> > > > > > the
> > > > > >    field order of a join output) are determinant and done
> entirely
> > at
> > > > an
> > > > > >    ordinal level. The only place where names should be used
> > (besides
> > > > > >    input/output) is in the case of map keys. In that case, the
> > names
> > > > are
> > > > > >    actually data, as opposed to scheme metadata. This is why I
> > propose
> > > > a
> > > > > >    strongly structured dereference operation [1].
> > > > > >    - Properties should only be included in the serialization if
> > they
> > > > are
> > > > > >    not easily re-derivable at plan consumption time. For example,
> > > > you'll
> > > > > > note
> > > > > >    that I don't store schema information for relational
> operation.
> > Each
> > > > > >    function and relational operation should already know how a
> > given
> > > > > input
> > > > > > is
> > > > > >    transformed to a given output. Capturing this information in
> the
> > > > > > plan/IR is
> > > > > >    excessive. In many ways, I compare it to the early use of
> > > > VectorLayout
> > > > > > [2]
> > > > > >    in Arrow schema. It may have provided some additional checksum
> > of
> > > > the
> > > > > >    message but ultimately it caused more pain than it was worth
> > (and
> > > > thus
> > > > > > we
> > > > > >    removed it before formalizing the specification). For
> > reference, in
> > > > > the
> > > > > >    context of Dremio, we used to actually do this, send schema
> > > > > information
> > > > > >    around for all operations. We removed it because in many cases
> > > > > becoming
> > > > > > the
> > > > > >    majority of our internal plan serialization (imagine simple
> > > > operations
> > > > > > that
> > > > > >    are carrying 1000s of fields).
> > > > > >    - I suggest focusing on support for both logical and physical
> > > > > >    representations. The moment you start talking about
> optimization
> > > > > passes,
> > > > > >    many of those would probably be better being done at the
> logical
> > > > > level.
> > > > > > The
> > > > > >    overlap is really high.
> > > > > >    - I think a lot more work must be done before introducing UDFs
> > and
> > > > > user
> > > > > >    defined relational operations. I see one goal being the
> > possibility
> > > > of
> > > > > >    there being three systems: A -> B -> C. A is a IR producer. C
> > is a
> > > > IR
> > > > > >    consumer and B is a IR filter or translator. In this
> situation,
> > B
> > > > > > should be
> > > > > >    able to operate and do optimizations on a plan even if if
> there
> > are
> > > > > > black
> > > > > >    box user defined operations. Being able to know the
> > > > > > properties-preservation
> > > > > >    or not of these operations is important to making decisions.
> For
> > > > > > example,
> > > > > >    does a user defined relational operation maintain sortedness?
> > > > > > Distribution?
> > > > > >    Is a defined UDF idempotent? As such, I think the definition
> of
> > > > those
> > > > > > black
> > > > > >    boxes should be much more structured. For example: it is a
> > python
> > > > > >    relational operation named X stored in Y that maintains
> > properties
> > > > 1,2
> > > > > > and
> > > > > >    disrupts property 3. Putting just a black box of bytes will
> > > > > > substantially
> > > > > >    reduce the compatibility and extensibility of the ecosystem of
> > tools
> > > > > >    working against IR. I'd note that I wouldn't expect this to
> be a
> > > > > burden
> > > > > > to
> > > > > >    actual end users. By using sensible defaults, I still would
> > expect
> > > > an
> > > > > > end
> > > > > >    user tool to support arbitrary user defined operations.
> > > > > >    - It might make sense to review the XML representation that
> Orca
> > > > uses
> > > > > >    [3]. I haven't looked at it recently but they had a strong
> goal
> > of
> > > > > >    decoupling for most of its life (to use in both Greenplum and
> > Hawq).
> > > > > It
> > > > > >    could be the most mature/formal serialization of query plans
> > > > > publically
> > > > > >    available.
> > > > > >
> > > > > >
> > > > > > [1]
> > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://github.com/apache/arrow/pull/10979/files#diff-e40fbc40cf7a131efd2cb098444931774cfad046b8665b38452258ffaa2e3423R34
> > > > > > [2]
> > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://github.com/apache/arrow/commit/611a4b951e24f4f967c3d382a2027dc035fc37f0
> > > > > > [3] https://github.com/greenplum-db/gporca
> > > > > >
> > > > > >
> > > > > > On Tue, Aug 17, 2021 at 11:14 AM Phillip Cloud <
> cpcloud@gmail.com>
> > > > > wrote:
> > > > > >
> > > > > > > On Tue, Aug 17, 2021 at 10:56 AM Wes McKinney <
> > wesmckinn@gmail.com>
> > > > > > wrote:
> > > > > > >
> > > > > > > > Looking at Ben's alternate PR [1], having an IR that leans
> > heavily
> > > > on
> > > > > > > > memory references to an out-of-band data sidecar seems like
> an
> > > > > > > > approach that would substantially ratchet up the
> implementation
> > > > > > > > complexity as producing the IR would then have the level of
> > > > > complexity
> > > > > > > > of producing the Arrow IPC format — when producing the "root"
> > Plan
> > > > > > > > message, you must accumulate a list of the dependent
> serialized
> > > > > > > > submessages, placing the appropriate Buffer memory offset in
> > the
> > > > Plan
> > > > > > > > message, like we do when producing the RecordBatch.buffers
> > field.
> > > > > This
> > > > > > > > seems complicated to me as you must devise a custom binary
> > protocol
> > > > > to
> > > > > > > > concatenate the serialized Plan and the messages it depends
> on
> > > > into a
> > > > > > > > single binary payload
> > > > > > > >
> > > > > > > > <ROOT PLAN>
> > > > > > > > <padding>
> > > > > > > > <Buffer 0>
> > > > > > > > <padding>
> > > > > > > > <Buffer 1>
> > > > > > > > <padding>
> > > > > > > > ...
> > > > > > > > <Buffer N - 1>
> > > > > > > >
> > > > > > > > (one purpose of FlatBufferBuilder is to spare you having to
> do
> > this
> > > > > > > > yourself — some reasons we do it for the Arrow IPC format is
> > > > because
> > > > > > > > appending Arrow memory buffers directly to a
> FlatBufferBuilder
> > > > would
> > > > > > > > be inefficient — internal realloc calls — and Flatbuffers are
> > > > limited
> > > > > > > > to 2GB. Neither of these things are problems here)
> > > > > > > >
> > > > > > > > In general, I believe the output created by an IR producer
> > should
> > > > be
> > > > > a
> > > > > > > > single serialized object without any out-of-band data
> sidecar —
> > > > this
> > > > > > > > is much simpler for implementers and we can still provide an
> > > > "escape
> > > > > > > > hatch" for user-defined operators and functions where the
> > required
> > > > > > > > function/operator is passed opaquely as an embedded binary
> > data.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > > The serialization format (whether it is Flatbuffers or JSON, or
> > > > > > > > something else) should allow for data memoization, so if
> there
> > is a
> > > > > > > > user-defined operator/function, or a relation that is used
> > multiple
> > > > > > > > times throughout the query (potentially with a large schema),
> > then
> > > > we
> > > > > > > > should ensure that the data need not be duplicated in the
> > > > > > > > serialization format unnecessarily — in Flatbuffers, you can
> > > > achieve
> > > > > > > > this by reusing offsets, but we could devise the data
> > structures to
> > > > > > > > make the memoization of "expensive" objects more explicit.
> > > > > > > >
> > > > > > >
> > > > > > > I think this is something that would need to be explicitly
> > encoded in
> > > > > > > the structures themselves if it's a hard requirement. I don't
> > think
> > > > > this
> > > > > > > should block
> > > > > > > a prototype producer/consumer.
> > > > > > >
> > > > > > > Is there something in the second PR/design that precludes the
> > reuse
> > > > of
> > > > > > > offsets?
> > > > > > > To my eye, the flatbuffers offset reuse mechanism works just as
> > well
> > > > > > there.
> > > > > > >
> > > > > > >
> > > > > > > > I additionally think that it is important to provide as much
> > > > built-in
> > > > > > > > support for "canonical" operators/functions (such as the ones
> > > > > > > > implemented commonly by SQL engines) as possible, and to
> > liberally
> > > > > > > > expand the catalogue of "built-in" capabilities. I would
> still
> > > > prefer
> > > > > > > > to have large unions/enums of built-in operators/functions
> and
> > to
> > > > > > > > expand those unions/enums to accommodate new things when it
> is
> > > > > > > > demonstrated that there is a need to standardize things
> between
> > > > > > > > producers/consumers.
> > > > > > > >
> > > > > > >
> > > > > > > I think there's a middle ground where we add a bit of structure
> > > > > > (something
> > > > > > > like
> > > > > > > a descriptor from the first PR) to indicate whether a thing is
> > > > built-in
> > > > > > vs
> > > > > > > user-defined.
> > > > > > > It looks like Ben has pushed something like this to his PR.
> > > > > > >
> > > > > > > With that scheme, we have both flexibility and a small set of
> > special
> > > > > > > builtins that make up
> > > > > > > a statically typed set for expressions and relational
> operators.
> > > > > > >
> > > > > > > I would really like to vet this PR with a prototype this week,
> > > > > > > to see whether we need to revisit any major choices. I don't
> > think
> > > > > we'll
> > > > > > be
> > > > > > > able to
> > > > > > > anticipate all the consequences until we write some code.
> > > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > One of the beneficial properties of the Union/Enum approach
> > for the
> > > > > > > > operator/function catalogues, is that when there are
> additions
> > to
> > > > > > > > those enums, the generated Flatbuffers files will cause many
> > > > language
> > > > > > > > compilers to warn or error on unhandled enum cases. If all
> > > > > > > > function/operator names are strings, then you are essentially
> > > > > > > > reimplementing the functionality provided by enums by hand. I
> > > > > > > > initially used strings for all function references in my
> > original
> > > > > > > > prototype, but I now think that using an enum for "built-ins"
> > would
> > > > > be
> > > > > > > > superior (because of the code-generated enum interface) and
> > not a
> > > > > > > > premature optimization.
> > > > > > > >
> > > > > > > > [1]: https://github.com/apache/arrow/pull/10934
> > > > > > > >
> > > > > > > > On Fri, Aug 13, 2021 at 11:26 PM Phillip Cloud <
> > cpcloud@gmail.com>
> > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > Hey all,
> > > > > > > > >
> > > > > > > > > Just wanted to give an update on the effort here.
> > > > > > > > >
> > > > > > > > > Ben Kietzman has created an alternative proposal to the
> > initial
> > > > > > design
> > > > > > > > [1].
> > > > > > > > > It largely overlaps with the original, but differs in a few
> > > > > important
> > > > > > > > ways:
> > > > > > > > >
> > > > > > > > > * A big focus of the design is on flexibility, allowing
> > > > producers,
> > > > > > > > > consumers and ultimately end users of those systems the
> > ability
> > > > to
> > > > > > > define
> > > > > > > > > custom operations in the graph.
> > > > > > > > > * There are very few predefined relational operations
> > (project,
> > > > > > filter,
> > > > > > > > > join and a handful of others).
> > > > > > > > > * There are only 3 types of value expressions: literals,
> > field
> > > > > > > > references,
> > > > > > > > > and function calls.
> > > > > > > > > * The model of evaluation is one that requires a final sink
> > node,
> > > > > to
> > > > > > > > > indicate where the record batches from child relations end
> > up (a
> > > > > > file,
> > > > > > > a
> > > > > > > > > socket, an in-memory buffer, etc).
> > > > > > > > >
> > > > > > > > > I've added notes [2] to the original Google doc (under the
> > > > > > Alternative
> > > > > > > > > Design Notes subheading), and a few pseudocode examples.
> > > > > > > > > Unfortunately, these went out of date as soon as Ben pushed
> > the
> > > > PR
> > > > > > [3],
> > > > > > > > so
> > > > > > > > > I need to update those to reflect his changes. Regardless,
> > > > > > > > > the design is broadly the same, so it should still give a
> > good
> > > > > > > indication
> > > > > > > > > of the details of the design.
> > > > > > > > >
> > > > > > > > > There are a decent number of review comments on the
> original
> > PR
> > > > > that
> > > > > > I
> > > > > > > > plan
> > > > > > > > > to port over where they are still relevant.
> > > > > > > > > I also plan on adding support for window functions either
> > tonight
> > > > > or
> > > > > > on
> > > > > > > > > Monday.
> > > > > > > > >
> > > > > > > > > Please review this design at your earliest convenience.
> Since
> > > > > > there's a
> > > > > > > > > fairly concrete set of types in flatbuffers that
> > > > > > > > > we can look at, ideally we can center discussion around the
> > > > details
> > > > > > in
> > > > > > > > the
> > > > > > > > > PR.
> > > > > > > > >
> > > > > > > > > Thanks!
> > > > > > > > >
> > > > > > > > > [1]: https://github.com/apache/arrow/pull/10856
> > > > > > > > > [2]:
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://docs.google.com/document/d/1C_XVOG7iFkl6cgWWMyzUoIjfKt-X2UxqagPJrla0bAE/edit#heading=h.4tfbbtaqzu13
> > > > > > > > > [3]: https://github.com/apache/arrow/pull/10934
> > > > > > > > >
> > > > > > > > > On Thu, Aug 12, 2021 at 3:55 PM Julian Hyde <
> > > > > jhyde.apache@gmail.com>
> > > > > > > > wrote:
> > > > > > > > >
> > > > > > > > > > > Wes wrote:
> > > > > > > > > > >
> > > > > > > > > > > Supporting this kind of intra-application engine
> > > > > > > > > > > heterogeneity is one of the motivations for the
> project.
> > > > > > > > > >
> > > > > > > > > > +1
> > > > > > > > > >
> > > > > > > > > > The data format is the natural interface between tasks.
> > > > (Defining
> > > > > > > > “task”
> > > > > > > > > > here as “something that is programmed using the IR”.)
> That
> > is
> > > > > > Arrow’s
> > > > > > > > > > strength.
> > > > > > > > > >
> > > > > > > > > > So I think the IR should describe what each task should
> > do, and
> > > > > > tasks
> > > > > > > > > > should be fairly small. Not whole relational operators,
> > > > operating
> > > > > > on
> > > > > > > > whole
> > > > > > > > > > tables, but pieces of relational operators, operating on
> > > > batches
> > > > > or
> > > > > > > > > > sequences of batches.
> > > > > > > > > >
> > > > > > > > > > Elsethread, someone mentioned the LoLePop concept and the
> > > > > > > > Kohn/Leis/Neuman
> > > > > > > > > > paper [1]. The LoLePop concept sounds good for our
> > purposes.
> > > > > > > > > >
> > > > > > > > > > Julian
> > > > > > > > > >
> > > > > > > > > > [1]
> > https://db.in.tum.de/~kohn/papers/lolepops-sigmod21.pdf
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > > > > > On Aug 12, 2021, at 5:19 AM, Wes McKinney <
> > > > wesmckinn@gmail.com
> > > > > >
> > > > > > > > wrote:
> > > > > > > > > > >
> > > > > > > > > > > On Wed, Aug 11, 2021 at 11:22 PM Phillip Cloud <
> > > > > > cpcloud@gmail.com>
> > > > > > > > > > wrote:
> > > > > > > > > > >>
> > > > > > > > > > >> On Wed, Aug 11, 2021 at 4:48 PM Jorge Cardoso Leitão <
> > > > > > > > > > >> jorgecarleitao@gmail.com> wrote:
> > > > > > > > > > >>
> > > > > > > > > > >>> Couple of questions
> > > > > > > > > > >>>
> > > > > > > > > > >>> 1. Is the goal that IRs have equal semantics, i.e.
> > given
> > > > > > > > (IR,data), the
> > > > > > > > > > >>> operation "(IR,data) - engine -> result" MUST be the
> > same
> > > > for
> > > > > > all
> > > > > > > > > > "engine"?
> > > > > > > > > > >>>
> > > > > > > > > > >>
> > > > > > > > > > >> I think that might be a non-starter for mundane
> reasons:
> > > > > there's
> > > > > > > > > > probably
> > > > > > > > > > >> at least two engines
> > > > > > > > > > >> that disagree on the result of sum(x) where x is a
> > floating
> > > > > > point
> > > > > > > > > > column.
> > > > > > > > > > >>
> > > > > > > > > > >>
> > > > > > > > > > >>> 2. if yes, imo we may need to worry about:
> > > > > > > > > > >>> * a definition of equality that implementations agree
> > on.
> > > > > > > > > > >>> * agreement over what the semantics look like. For
> > example,
> > > > > do
> > > > > > we
> > > > > > > > use
> > > > > > > > > > >>> kleene logic for AND and OR?
> > > > > > > > > > >>>
> > > > > > > > > > >>
> > > > > > > > > > >> WRT Kleene logic my thoughts are that the IR should
> > support
> > > > > both
> > > > > > > > Kleene
> > > > > > > > > > and
> > > > > > > > > > >> non-Kleene,
> > > > > > > > > > >> and producers can choose their desired semantics.
> > > > > > > > > > >>
> > > > > > > > > > >> Ibis for example, would override the `&` operator in
> `a
> > & b`
> > > > > to
> > > > > > > > produce
> > > > > > > > > > >> `KleeneAnd(Column(a), Column(b))`.
> > > > > > > > > > >>
> > > > > > > > > > >>
> > > > > > > > > > >>>
> > > > > > > > > > >>> To try to understand the gist, let's pick an
> aggregated
> > > > count
> > > > > > > over
> > > > > > > > a
> > > > > > > > > > >>> column: engines often do partial counts over
> partitions
> > > > > > followed
> > > > > > > > by a
> > > > > > > > > > final
> > > > > > > > > > >>> "sum" over the partial counts. Is the idea that the
> > query
> > > > > > engine
> > > > > > > > would
> > > > > > > > > > >>> communicate with the compute engine via 2 IRs where
> > one is
> > > > > > "count
> > > > > > > > me
> > > > > > > > > > these"
> > > > > > > > > > >>> the other is "sum me these"?
> > > > > > > > > > >>>
> > > > > > > > > > >>> Best,
> > > > > > > > > > >>> Jorge
> > > > > > > > > > >>>
> > > > > > > > > > >>
> > > > > > > > > > >> Not in its current incarnation.
> > > > > > > > > > >>
> > > > > > > > > > >> The idea is that the IR producer communicates a desire
> > to
> > > > > > count(x)
> > > > > > > > to a
> > > > > > > > > > >> consumer, and  it's up to the consumer to figure out
> > how to
> > > > > turn
> > > > > > > > that
> > > > > > > > > > count
> > > > > > > > > > >> into something that makes sense for itself. In your
> > example
> > > > > > > that's a
> > > > > > > > > > series
> > > > > > > > > > >> of partial counts followed by a sum.
> > > > > > > > > > >>
> > > > > > > > > > >
> > > > > > > > > > > That said, I think there is a valid use case here
> where a
> > > > > system
> > > > > > > > might
> > > > > > > > > > > make use of different engines to execute different
> > > > (composable)
> > > > > > > > layers
> > > > > > > > > > > of a complex query.
> > > > > > > > > > >
> > > > > > > > > > > For example:
> > > > > > > > > > >
> > > > > > > > > > > * suppose you want to scan and do predicate pushdown on
> > an
> > > > > > unusual
> > > > > > > > > > > data source that is only accessible from one particular
> > > > engine
> > > > > > but
> > > > > > > > > > > * you need to do some analytical operation with the
> scan
> > > > > results
> > > > > > > that
> > > > > > > > > > > is only supported by another engine
> > > > > > > > > > >
> > > > > > > > > > > You could decompose the query into two stages with an
> IR
> > > > > > relational
> > > > > > > > > > > expression for each stage and use then the engines
> > together
> > > > to
> > > > > > > > > > > accomplish what you need (of course, you would need an
> > > > > > > orchestration
> > > > > > > > > > > layer to handle plumbing the query engine inputs and
> > outputs
> > > > > > > together
> > > > > > > > > > > as Arrow streams). Supporting this kind of
> > intra-application
> > > > > > engine
> > > > > > > > > > > heterogeneity is one of the motivations for the
> project.
> > > > > > > > > > >
> > > > > > > > > > >>>
> > > > > > > > > > >>>
> > > > > > > > > > >>>
> > > > > > > > > > >>>
> > > > > > > > > > >>>
> > > > > > > > > > >>> On Wed, Aug 11, 2021 at 6:10 PM Phillip Cloud <
> > > > > > cpcloud@gmail.com
> > > > > > > >
> > > > > > > > > > wrote:
> > > > > > > > > > >>>
> > > > > > > > > > >>>> Thanks Wes,
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Great to be back working on Arrow again and engaging
> > with
> > > > > the
> > > > > > > > > > community.
> > > > > > > > > > >>> I
> > > > > > > > > > >>>> am really excited about this effort.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> I think there are a number of concerns I see as
> > important
> > > > to
> > > > > > > > address
> > > > > > > > > > in
> > > > > > > > > > >>> the
> > > > > > > > > > >>>> compute IR proposal:
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 1. Requirement for output types.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> I think that so far there's been many reasons for
> > > > requiring
> > > > > > > > > > conforming IR
> > > > > > > > > > >>>> producers and consumers to adhere to output types,
> > but I
> > > > > > haven't
> > > > > > > > seen
> > > > > > > > > > a
> > > > > > > > > > >>>> strong rationale for keeping them optional (in the
> > > > semantic
> > > > > > > > sense, not
> > > > > > > > > > >>> WRT
> > > > > > > > > > >>>> any particular serialization format's representation
> > of
> > > > > > > > optionality).
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> I think a design that includes unambiguous semantics
> > for
> > > > > > output
> > > > > > > > types
> > > > > > > > > > (a
> > > > > > > > > > >>>> consumer must produce a value of the requested type
> or
> > > > it's
> > > > > an
> > > > > > > > > > >>>> error/non-conforming) is simpler to reason about for
> > > > > > producers,
> > > > > > > > and
> > > > > > > > > > >>>> provides a strong guarantee for end users (humans or
> > > > > machines
> > > > > > > > > > >>> constructing
> > > > > > > > > > >>>> IR from an API and expecting the thing they ask for
> > back
> > > > > from
> > > > > > > the
> > > > > > > > IR
> > > > > > > > > > >>>> consumer).
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 2. Flexibility
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> The current PR is currently unable to support what I
> > think
> > > > > are
> > > > > > > > killer
> > > > > > > > > > >>>> features of the IR: custom operators (relational or
> > > > column)
> > > > > > and
> > > > > > > > UDFs.
> > > > > > > > > > In
> > > > > > > > > > >>> my
> > > > > > > > > > >>>> mind, on top of the generalized compute description
> > that
> > > > the
> > > > > > IR
> > > > > > > > > > offers,
> > > > > > > > > > >>> the
> > > > > > > > > > >>>> ability for producers and consumers of IR to extend
> > the IR
> > > > > > > without
> > > > > > > > > > >>> needing
> > > > > > > > > > >>>> to modify Arrow or depend on anything except the
> > format is
> > > > > > > itself
> > > > > > > > > > >>> something
> > > > > > > > > > >>>> that is necessary to gain adoption.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Developers will need to build custom relational
> > operators
> > > > > > (e.g.,
> > > > > > > > > > scans of
> > > > > > > > > > >>>> backends that don't exist anywhere for which a user
> > has
> > > > code
> > > > > > to
> > > > > > > > > > >>> implement)
> > > > > > > > > > >>>> and custom functions (anything operating on a column
> > that
> > > > > > > doesn't
> > > > > > > > > > already
> > > > > > > > > > >>>> exist, really). Furthermore, I think we can actually
> > drive
> > > > > > > > building an
> > > > > > > > > > >>>> Arrow consumer using the same API that an end user
> > would
> > > > use
> > > > > > to
> > > > > > > > extend
> > > > > > > > > > >>> the
> > > > > > > > > > >>>> IR.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 3. Window Functions
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Window functions are, I think, an important part of
> > the IR
> > > > > > value
> > > > > > > > > > >>>> proposition, as they are one of the more complex
> > operators
> > > > > in
> > > > > > > > > > databases.
> > > > > > > > > > >>> I
> > > > > > > > > > >>>> think we need to have something in the initial IR
> > proposal
> > > > > to
> > > > > > > > support
> > > > > > > > > > >>> these
> > > > > > > > > > >>>> operations.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 4. Non relational Joins
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Things like as-of join and window join operators
> > aren't
> > > > yet
> > > > > > > > fleshed
> > > > > > > > > > out
> > > > > > > > > > >>> in
> > > > > > > > > > >>>> the IR, and I'm not sure they should be in scope for
> > the
> > > > > > initial
> > > > > > > > > > >>> prototype.
> > > > > > > > > > >>>> I think once we settle on a design, we can work the
> > design
> > > > > of
> > > > > > > > these
> > > > > > > > > > >>>> particular operators out during the initial
> > prototype. I
> > > > > think
> > > > > > > the
> > > > > > > > > > >>>> specification of these operators should basically be
> > PR #2
> > > > > > after
> > > > > > > > the
> > > > > > > > > > >>>> initial design lands.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> # Order of Work
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 1. Nail down the design. Anything else is a
> > non-starter.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 2. Prototype an IR producer using Ibis
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Ibis is IMO a good candidate for a first IR producer
> > as it
> > > > > > has a
> > > > > > > > > > number
> > > > > > > > > > >>> of
> > > > > > > > > > >>>> desirable properties that make prototyping faster
> and
> > > > allow
> > > > > > for
> > > > > > > > us to
> > > > > > > > > > >>>> refine the design of the IR as needed based on how
> the
> > > > > > > > implementation
> > > > > > > > > > >>> goes:
> > > > > > > > > > >>>> * It's written in Python so it has native support
> for
> > > > nearly
> > > > > > all
> > > > > > > > of
> > > > > > > > > > >>>> flatbuffers' features without having to creating
> > bindings
> > > > to
> > > > > > > C++.
> > > > > > > > > > >>>> * There's already a set of rules for type checking,
> as
> > > > well
> > > > > as
> > > > > > > > APIs
> > > > > > > > > > for
> > > > > > > > > > >>>> constructing expression trees, which means we don't
> > need
> > > > to
> > > > > > > worry
> > > > > > > > > > about
> > > > > > > > > > >>>> building a type checker for the prototype.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> 3. Prototype an IR consumer in C++
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> I think in parallel to the producer prototype we can
> > > > further
> > > > > > > > inform
> > > > > > > > > > the
> > > > > > > > > > >>>> design from the consumer side by prototyping an IR
> > > > consumer
> > > > > in
> > > > > > > > C++ . I
> > > > > > > > > > >>> know
> > > > > > > > > > >>>> Ben Kietzman has expressed interest in working on
> > this.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> Very interested to hear others' thoughts.
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> -Phillip
> > > > > > > > > > >>>>
> > > > > > > > > > >>>> On Tue, Aug 10, 2021 at 10:56 AM Wes McKinney <
> > > > > > > > wesmckinn@gmail.com>
> > > > > > > > > > >>> wrote:
> > > > > > > > > > >>>>
> > > > > > > > > > >>>>> Thank you for all the feedback and comments on the
> > > > > document.
> > > > > > > I'm
> > > > > > > > on
> > > > > > > > > > >>>>> vacation this week, so I'm delayed responding to
> > > > > everything,
> > > > > > > but
> > > > > > > > I
> > > > > > > > > > >>>>> will get to it as quickly as I can. I will be at
> > VLDB in
> > > > > > > > Copenhagen
> > > > > > > > > > >>>>> next week if anyone would like to chat in person
> > about
> > > > it,
> > > > > > and
> > > > > > > > we can
> > > > > > > > > > >>>>> relay the content of any discussions back to the
> > > > > > > > document/PR/e-mail
> > > > > > > > > > >>>>> thread.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> I know that Phillip Cloud expressed interest in
> > working
> > > > on
> > > > > > the
> > > > > > > > PR and
> > > > > > > > > > >>>>> helping work through many of the details, so I'm
> > glad to
> > > > > have
> > > > > > > the
> > > > > > > > > > >>>>> help. If there are others who would like to work on
> > the
> > > > PR
> > > > > or
> > > > > > > dig
> > > > > > > > > > into
> > > > > > > > > > >>>>> the details, please let me know. We might need to
> > figure
> > > > > out
> > > > > > > how
> > > > > > > > to
> > > > > > > > > > >>>>> accommodate "many cooks" by setting up the
> ComputeIR
> > > > > project
> > > > > > > > > > somewhere
> > > > > > > > > > >>>>> separate from the format/ directory to permit it to
> > exist
> > > > > in
> > > > > > a
> > > > > > > > > > >>>>> Work-In-Progress status for a period of time until
> we
> > > > work
> > > > > > > > through
> > > > > > > > > > the
> > > > > > > > > > >>>>> various details and design concerns.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> Re Julian's comment
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>>> The biggest surprise is that this language does
> full
> > > > > > > relational
> > > > > > > > > > >>>>> operations. I was expecting that it would do
> > fragments of
> > > > > the
> > > > > > > > > > >>> operations.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> There's a related but different (yet still
> > interesting
> > > > and
> > > > > > > > worthy of
> > > > > > > > > > >>>>> analysis) problem of creating an "engine language"
> > that
> > > > > > > describes
> > > > > > > > > > more
> > > > > > > > > > >>>>> mechanically the constituent parts of implementing
> > the
> > > > > > > relational
> > > > > > > > > > >>>>> operators. To create a functional computation
> > language
> > > > with
> > > > > > > > concrete
> > > > > > > > > > >>>>> Arrow data structures as a top-level primitive
> sounds
> > > > like
> > > > > an
> > > > > > > > > > >>>>> interesting research area where I could see
> something
> > > > > > > developing
> > > > > > > > > > >>>>> eventually.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> The main problem I'm interested in solving right
> now
> > is
> > > > > > > enabling
> > > > > > > > > > front
> > > > > > > > > > >>>>> ends that have sufficient understanding of
> relational
> > > > > algebra
> > > > > > > and
> > > > > > > > > > data
> > > > > > > > > > >>>>> frame operations to talk to engines without having
> > to go
> > > > > > > > backwards
> > > > > > > > > > >>>>> from their logical query plans to SQL. So as
> > mentioned in
> > > > > the
> > > > > > > > > > >>>>> document, being able to faithfully carry the
> > relational
> > > > > > > operator
> > > > > > > > node
> > > > > > > > > > >>>>> information generated by Calcite or Ibis or another
> > > > system
> > > > > > > would
> > > > > > > > be
> > > > > > > > > > >>>>> super useful. Defining the semantics of various
> > kinds of
> > > > > > > > user-defined
> > > > > > > > > > >>>>> functions would also be helpful to standardize the
> > > > > > > > > > >>>>> engine-to-user-language UDF/extension interface.
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>> On Tue, Aug 10, 2021 at 2:36 PM Dimitri Vorona <
> > > > > > > > alendit@gmail.com>
> > > > > > > > > > >>>> wrote:
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> Hi Wes,
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> cool initiative! Reminded me of "Building Advanced
> > SQL
> > > > > > > Analytics
> > > > > > > > > > From
> > > > > > > > > > >>>>>> Low-Level Plan Operators" from SIGMOD 2021 (
> > > > > > > > > > >>>>>>
> > http://db.in.tum.de/~kohn/papers/lolepops-sigmod21.pdf)
> > > > > > which
> > > > > > > > > > >>>> proposes a
> > > > > > > > > > >>>>>> set of building block for advanced aggregation.
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> Cheers,
> > > > > > > > > > >>>>>> Dimitri.
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>> On Thu, Aug 5, 2021 at 7:59 PM Julian Hyde <
> > > > > > > > jhyde.apache@gmail.com>
> > > > > > > > > > >>>>> wrote:
> > > > > > > > > > >>>>>>
> > > > > > > > > > >>>>>>> Wes,
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>> Thanks for this. I’ve added comments to the doc
> > and to
> > > > > the
> > > > > > > PR.
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>> The biggest surprise is that this language does
> > full
> > > > > > > relational
> > > > > > > > > > >>>>>>> operations. I was expecting that it would do
> > fragments
> > > > of
> > > > > > the
> > > > > > > > > > >>>>> operations.
> > > > > > > > > > >>>>>>> Consider join. A distributed hybrid hash join
> > needs to
> > > > > > > > partition
> > > > > > > > > > >>> rows
> > > > > > > > > > >>>>> into
> > > > > > > > > > >>>>>>> output buffers based on a hash key, build hash
> > tables,
> > > > > > probe
> > > > > > > > into
> > > > > > > > > > >>>> hash
> > > > > > > > > > >>>>>>> tables, scan hash tables for untouched
> > “outer”rows, and
> > > > > so
> > > > > > > > forth.
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>> I see Arrow’s compute as delivering each of those
> > > > > > operations,
> > > > > > > > > > >>> working
> > > > > > > > > > >>>>> on
> > > > > > > > > > >>>>>>> perhaps a batch at a time, or a sequence of
> > batches,
> > > > with
> > > > > > > some
> > > > > > > > > > >>> other
> > > > > > > > > > >>>>> system
> > > > > > > > > > >>>>>>> coordinating those tasks. So I would expect to
> see
> > > > > Arrow’s
> > > > > > > > compute
> > > > > > > > > > >>>>> language
> > > > > > > > > > >>>>>>> mainly operating on batches rather than a table
> > > > > > abstraction.
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>> Julian
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>>> On Aug 2, 2021, at 5:16 PM, Wes McKinney <
> > > > > > > wesmckinn@gmail.com
> > > > > > > > >
> > > > > > > > > > >>>>> wrote:
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> hi folks,
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> This idea came up in passing in the past --
> given
> > that
> > > > > > there
> > > > > > > > are
> > > > > > > > > > >>>>>>>> multiple independent efforts to develop
> > Arrow-native
> > > > > query
> > > > > > > > > > >>> engines
> > > > > > > > > > >>>>>>>> (and surely many more to come), it seems like it
> > would
> > > > > be
> > > > > > > > > > >>> valuable
> > > > > > > > > > >>>> to
> > > > > > > > > > >>>>>>>> have a way to enable user languages (like Java,
> > > > Python,
> > > > > R,
> > > > > > > or
> > > > > > > > > > >>> Rust,
> > > > > > > > > > >>>>>>>> for example) to communicate with backend
> computing
> > > > > engines
> > > > > > > > (like
> > > > > > > > > > >>>>>>>> DataFusion, or new computing capabilities being
> > built
> > > > in
> > > > > > the
> > > > > > > > > > >>> Arrow
> > > > > > > > > > >>>>> C++
> > > > > > > > > > >>>>>>>> library) in a fashion that is "lower-level" than
> > SQL
> > > > and
> > > > > > > > > > >>>> specialized
> > > > > > > > > > >>>>>>>> to Arrow's type system. So rather than leaving
> it
> > to a
> > > > > SQL
> > > > > > > > > > >>> parser /
> > > > > > > > > > >>>>>>>> analyzer framework to generate an expression
> tree
> > of
> > > > > > > > relational
> > > > > > > > > > >>>>>>>> operators and then translate that to an
> > Arrow-native
> > > > > > > > > > >>>> compute-engine's
> > > > > > > > > > >>>>>>>> internal grammer, a user framework could provide
> > the
> > > > > > desired
> > > > > > > > > > >>>>>>>> Arrow-native expression tree / data
> manipulations
> > > > > directly
> > > > > > > and
> > > > > > > > > > >>> skip
> > > > > > > > > > >>>>>>>> the SQL altogether.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> The idea of creating a "serialized intermediate
> > > > > > > representation
> > > > > > > > > > >>>> (IR)"
> > > > > > > > > > >>>>>>>> for Arrow compute operations would be to serve
> use
> > > > cases
> > > > > > > large
> > > > > > > > > > >>> and
> > > > > > > > > > >>>>>>>> small -- from the most complex TPC-* or time
> > series
> > > > > > database
> > > > > > > > > > >>> query
> > > > > > > > > > >>>> to
> > > > > > > > > > >>>>>>>> the most simple array predicate/filter sent with
> > an
> > > > RPC
> > > > > > > > request
> > > > > > > > > > >>>> using
> > > > > > > > > > >>>>>>>> Arrow Flight. It is deliberately language- and
> > > > > > > > engine-agnostic,
> > > > > > > > > > >>>> with
> > > > > > > > > > >>>>>>>> the only commonality across usages being the
> Arrow
> > > > > > columnar
> > > > > > > > > > >>> format
> > > > > > > > > > >>>>>>>> (schemas and array types). This would be better
> > than
> > > > > > leaving
> > > > > > > > it
> > > > > > > > > > >>> to
> > > > > > > > > > >>>>>>>> each application to develop its own bespoke
> > expression
> > > > > > > > > > >>>>> representations
> > > > > > > > > > >>>>>>>> for its needs.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> I spent a while thinking about this and wrote
> up a
> > > > brain
> > > > > > > dump
> > > > > > > > RFC
> > > > > > > > > > >>>>>>>> document [1] and accompanying pull request [2]
> > that
> > > > > makes
> > > > > > > the
> > > > > > > > > > >>>>> possibly
> > > > > > > > > > >>>>>>>> controversial choice of using Flatbuffers to
> > represent
> > > > > the
> > > > > > > > > > >>>> serialized
> > > > > > > > > > >>>>>>>> IR. I discuss the rationale for the choice of
> > > > > Flatbuffers
> > > > > > in
> > > > > > > > the
> > > > > > > > > > >>>> RFC
> > > > > > > > > > >>>>>>>> document. This PR is obviously deficient in many
> > > > regards
> > > > > > > > > > >>>> (incomplete,
> > > > > > > > > > >>>>>>>> hacky, or unclear in places), and will need some
> > help
> > > > > from
> > > > > > > > others
> > > > > > > > > > >>>> to
> > > > > > > > > > >>>>>>>> flesh out. I suspect that actually implementing
> > the IR
> > > > > > will
> > > > > > > be
> > > > > > > > > > >>>>>>>> necessary to work out many of the low-level
> > details.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> Note that this IR is intended to be more of a
> > > > "superset"
> > > > > > > > project
> > > > > > > > > > >>>> than
> > > > > > > > > > >>>>>>>> a "lowest common denominator". So there may be
> > things
> > > > > that
> > > > > > > it
> > > > > > > > > > >>>>> includes
> > > > > > > > > > >>>>>>>> which are only available in some engines (e.g.
> > engines
> > > > > > that
> > > > > > > > have
> > > > > > > > > > >>>>>>>> specialized handling of time series data).
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> As some of my personal motivation for the
> project,
> > > > > > > concurrent
> > > > > > > > > > >>> with
> > > > > > > > > > >>>>> the
> > > > > > > > > > >>>>>>>> genesis of Apache Arrow, I started a Python
> > project
> > > > > called
> > > > > > > > Ibis
> > > > > > > > > > >>> [3]
> > > > > > > > > > >>>>>>>> (which is similar to R's dplyr project) which
> > serves
> > > > as
> > > > > a
> > > > > > > > "Python
> > > > > > > > > > >>>>>>>> analytical query IR builder" that is capable of
> > > > > generating
> > > > > > > > most
> > > > > > > > > > >>> of
> > > > > > > > > > >>>>> the
> > > > > > > > > > >>>>>>>> SQL standard, targeting many different SQL
> > dialects
> > > > and
> > > > > > > other
> > > > > > > > > > >>>>> backends
> > > > > > > > > > >>>>>>>> (like pandas). Microsoft ([4]) and Google ([5])
> > have
> > > > > used
> > > > > > > this
> > > > > > > > > > >>>>> library
> > > > > > > > > > >>>>>>>> as a "many-SQL" middleware. As such, I would
> like
> > to
> > > > be
> > > > > > able
> > > > > > > > to
> > > > > > > > > > >>>>>>>> translate between the in-memory "logical query"
> > data
> > > > > > > > structures
> > > > > > > > > > >>> in
> > > > > > > > > > >>>> a
> > > > > > > > > > >>>>>>>> library like Ibis to a serialized format that
> can
> > be
> > > > > > > executed
> > > > > > > > by
> > > > > > > > > > >>>> many
> > > > > > > > > > >>>>>>>> different Arrow-native query engines. The
> > expression
> > > > > > > > primitives
> > > > > > > > > > >>>>>>>> available in Ibis should serve as helpful test
> > cases,
> > > > > too.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> I look forward to the community's comments on
> the
> > RFC
> > > > > > > document
> > > > > > > > > > >>> [1]
> > > > > > > > > > >>>>> and
> > > > > > > > > > >>>>>>>> pull request [2] -- I realize that arriving at
> > > > consensus
> > > > > > on
> > > > > > > a
> > > > > > > > > > >>>> complex
> > > > > > > > > > >>>>>>>> and ambitious project like this can be
> > challenging so
> > > > I
> > > > > > > > recommend
> > > > > > > > > > >>>>>>>> spending time on the "non-goals" section in the
> > RFC
> > > > and
> > > > > > ask
> > > > > > > > > > >>>> questions
> > > > > > > > > > >>>>>>>> if you are unclear about the scope of what
> > problems
> > > > this
> > > > > > is
> > > > > > > > > > >>> trying
> > > > > > > > > > >>>> to
> > > > > > > > > > >>>>>>>> solve. I would be happy to give Edit access on
> > the RFC
> > > > > > > > document
> > > > > > > > > > >>> to
> > > > > > > > > > >>>>>>>> others and would consider ideas about how to
> move
> > > > > forward
> > > > > > > with
> > > > > > > > > > >>>>>>>> something that is able to be implemented by
> > different
> > > > > > Arrow
> > > > > > > > > > >>>> libraries
> > > > > > > > > > >>>>>>>> in the reasonably near future.
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> Thanks,
> > > > > > > > > > >>>>>>>> Wes
> > > > > > > > > > >>>>>>>>
> > > > > > > > > > >>>>>>>> [1]:
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>
> > > > > > > > > > >>>
> > > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://docs.google.com/document/d/1C_XVOG7iFkl6cgWWMyzUoIjfKt-X2UxqagPJrla0bAE/edit#
> > > > > > > > > > >>>>>>>> [2]: https://github.com/apache/arrow/pull/10856
> > > > > > > > > > >>>>>>>> [3]: https://ibis-project.org/
> > > > > > > > > > >>>>>>>> [4]:
> > > > > > http://cidrdb.org/cidr2021/papers/cidr2021_paper08.pdf
> > > > > > > > > > >>>>>>>> [5]:
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>
> > > > > > > > > > >>>
> > > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> https://cloud.google.com/blog/products/databases/automate-data-validation-with-dvt
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>>>
> > > > > > > > > > >>>>>
> > > > > > > > > > >>>>
> > > > > > > > > > >>>
> > > > > > > > > >
> > > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> >
> >
>