Re: Spurious test failures, testing best practices

["York, Brennon" <Br...@capitalone.com>]

+1, you aren¹t alone in this. I certainly would like some clarity in these
things well, but, as its been said on this listserv a few times (and you
noted), most developers use `sbt` for their day-to-day compilations to
greatly speed up the iterative testing process. I personally use `sbt` for
all builds until I¹m ready to submit a PR and *then* run ./dev/run-tests
to ensure all the tests / code I¹ve written still pass (i.e. nothing
breaks in the code I¹ve changed or downstream). Sometimes, like you¹ve
said, you still get errors with the ./dev/run-tests script, but, for me,
it comes down to where the errors initiate from and whether I¹m confident
the code I wrote caused it or not as the delimiter to whether I submit the
PR.

Again, not a great answer and hoping others can shed more light, but thats
my 2c on the problem.

On 11/30/14, 5:39 PM, "Ryan Williams" <ry...@gmail.com>
wrote:

>In the course of trying to make contributions to Spark, I have had a lot
>of
>trouble running Spark's tests successfully. The main pain points I've
>experienced are:
>
>    1) frequent, spurious test failures
>    2) high latency of running tests
>    3) difficulty running specific tests in an iterative fashion
>
>Here is an example series of failures that I encountered this weekend
>(along with footnote links to the console output from each and
>approximately how long each took):
>
>- `./dev/run-tests` [1]: failure in BroadcastSuite that I've not seen
>before.
>- `mvn '-Dsuites=*BroadcastSuite*' test` [2]: same failure.
>- `mvn '-Dsuites=*BroadcastSuite* Unpersisting' test` [3]: BroadcastSuite
>passed, but scala compiler crashed on the "catalyst" project.
>- `mvn clean`: some attempts to run earlier commands (that previously
>didn't crash the compiler) all result in the same compiler crash. Previous
>discussion on this list implies this can only be solved by a `mvn clean`
>[4].
>- `mvn '-Dsuites=*BroadcastSuite*' test` [5]: immediately post-clean,
>BroadcastSuite can't run because assembly is not built.
>- `./dev/run-tests` again [6]: pyspark tests fail, some messages about
>version mismatches and python 2.6. The machine this ran on has python 2.7,
>so I don't know what that's about.
>- `./dev/run-tests` again [7]: "too many open files" errors in several
>tests. `ulimit -a` shows a maximum of 4864 open files. Apparently this is
>not enough, but only some of the time? I increased it to 8192 and tried
>again.
>- `./dev/run-tests` again [8]: same pyspark errors as before. This seems
>to
>be the issue from SPARK-3867 [9], which was supposedly fixed on October
>14;
>not sure how I'm seeing it now. In any case, switched to Python 2.6 and
>installed unittest2, and python/run-tests seems to be unblocked.
>- `./dev/run-tests` again [10]: finally passes!
>
>This was on a spark checkout at ceb6281 (ToT Friday), with a few trivial
>changes added on (that I wanted to test before sending out a PR), on a
>macbook running OSX Yosemite (10.10.1), java 1.8 and mvn 3.2.3 [11].
>
>Meanwhile, on a linux 2.6.32 / CentOS 6.4 machine, I tried similar
>commands
>from the same repo state:
>
>- `./dev/run-tests` [12]: YarnClusterSuite failure.
>- `./dev/run-tests` [13]: same YarnClusterSuite failure. I know I've seen
>this one before on this machine and am guessing it actually occurs every
>time.
>- `./dev/run-tests` [14]: to be sure, I reverted my changes, ran one more
>time from ceb6281, and saw the same failure.
>
>This was with java 1.7 and maven 3.2.3 [15]. In one final attempt to
>narrow
>down the linux YarnClusterSuite failure, I ran `./dev/run-tests` on my
>mac,
>from ceb6281, with java 1.7 (instead of 1.8, which the previous runs
>used),
>and it passed [16], so the failure seems specific to my linux
>machine/arch.
>
>At this point I believe that my changes don't break any tests (the
>YarnClusterSuite failure on my linux presumably not being... "real"), and
>I
>am ready to send out a PR. Whew!
>
>However, reflecting on the 5 or 6 distinct failure-modes represented
>above:
>
>- One of them (too many files open), is something I can (and did,
>hopefully) fix once and for all. It cost me an ~hour this time
>(approximate
>time of running ./dev/run-tests) and a few hours other times when I didn't
>fully understand/fix it. It doesn't happen deterministically (why?), but
>does happen somewhat frequently to people, having been discussed on the
>user list multiple times [17] and on SO [18]. Maybe some note in the
>documentation advising people to check their ulimit makes sense?
>- One of them (unittest2 must be installed for python 2.6) was supposedly
>fixed upstream of the commits I tested here; I don't know why I'm still
>running into it. This cost me a few hours of running `./dev/run-tests`
>multiple times to see if it was transient, plus some time researching and
>working around it.
>- The original BroadcastSuite failure cost me a few hours and went away
>before I'd even run `mvn clean`.
>- A new incarnation of the sbt-compiler-crash phenomenon cost me a few
>hours of running `./dev/run-tests` in different ways before deciding that,
>as usual, there was no way around it and that I'd need to run `mvn clean`
>and start running tests from scratch.
>- The YarnClusterSuite failures on my linux box have cost me hours of
>trying to figure out whether they're my fault. I've seen them many times
>over the past weeks/months, plus or minus other failures that have come
>and
>gone, and was especially befuddled by them when I was seeing a disjoint
>set
>of reproducible failures on my mac [19] (the triaging of which involved
>dozens of runs of `./dev/run-tests`).
>
>While I'm interested in digging into each of these issues, I also want to
>discuss the frequency with which I've run into issues like these. This is
>unfortunately not the first time in recent months that I've spent days
>playing spurious-test-failure whack-a-mole with a 60-90min dev/run-tests
>iteration time, which is no fun! So I am wondering/thinking:
>
>- Do other people experience this level of flakiness from spark tests?
>- Do other people bother running dev/run-tests locally, or just let
>Jenkins
>do it during the CR process?
>- Needing to run a full assembly post-clean just to continue running one
>specific test case feels especially wasteful, and the failure output when
>naively attempting to run a specific test without having built an assembly
>jar is not always clear about what the issue is or how to fix it; even the
>fact that certain tests require "building the world" is not something I
>would have expected, and has cost me hours of confusion.
>    - Should a person running spark tests assume that they must build an
>assembly JAR before running anything?
>    - Are there some proper "unit" tests that are actually self-contained
>/
>able to be run without building an assembly jar?
>    - Can we better document/demarcate which tests have which
>dependencies?
>    - Is there something finer-grained than building an assembly JAR that
>is sufficient in some cases?
>        - If so, can we document that?
>        - If not, can we move to a world of finer-grained dependencies for
>some of these?
>- Leaving all of these spurious failures aside, the process of assembling
>and testing a new JAR is not a quick one (40 and 60 mins for me typically,
>respectively). I would guess that there are dozens (hundreds?) of people
>who build a Spark assembly from various ToTs on any given day, and who all
>wait on the exact same compilation / assembly steps to occur. Expanding on
>the recent work to publish nightly snapshots [20], can we do a better job
>caching/sharing compilation artifacts at a more granular level (pre-built
>assembly JARs at each SHA? pre-built JARs per-maven-module, per-SHA? more
>granular maven modules, plus the previous two?), or otherwise save some of
>the considerable amount of redundant compilation work that I had to do
>over
>the course of my odyssey this weekend?
>
>Ramping up on most projects involves some amount of supplementing the
>documentation with trial and error to figure out what to run, which
>"errors" are real errors and which can be ignored, etc., but navigating
>that minefield on Spark has proved especially challenging and
>time-consuming for me. Some of that comes directly from scala's relatively
>slow compilation times and immature build-tooling ecosystem, but that is
>the world we live in and it would be nice if Spark took the alleviation of
>the resulting pain more seriously, as one of the more interesting and
>well-known large scala projects around right now. The official
>documentation around how to build different subsets of the codebase is
>somewhat sparse [21], and there have been many mixed [22] accounts [23] on
>this mailing list about preferred ways to build on mvn vs. sbt (none of
>which has made it into official documentation, as far as I've seen).
>Expecting new contributors to piece together all of this received
>folk-wisdom about how to build/test in a sane way by trawling mailing list
>archives seems suboptimal.
>
>Thanks for reading, looking forward to hearing your ideas!
>
>-Ryan
>
>P.S. Is "best practice" for emailing this list to not incorporate any HTML
>in the body? It seems like all of the archives I've seen strip it out, but
>other people have used it and gmail displays it.
>
>
>[1]
>https://gist.githubusercontent.com/ryan-williams/8a162367c4dc157d2479/raw/
>484c2fb8bc0efa0e39d142087eefa9c3d5292ea3/dev%20run-tests:%20fail
>(57 mins)
>[2]
>https://gist.githubusercontent.com/ryan-williams/8a162367c4dc157d2479/raw/
>ce264e469be3641f061eabd10beb1d71ac243991/mvn%20test:%20fail
>(6 mins)
>[3]
>https://gist.githubusercontent.com/ryan-williams/8a162367c4dc157d2479/raw/
>6bc76c67aeef9c57ddd9fb2ba260fb4189dbb927/mvn%20test%20case:%20pass%20test,
>%20fail%20subsequent%20compile
>(4 mins)
>[4]
>https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCUQF
>jAB&url=http%3A%2F%2Fapache-spark-user-list.1001560.n3.nabble.com%2Fscalac
>-crash-when-compiling-DataTypeConversions-scala-td17083.html&ei=aRF6VJrpNK
>r-iAKDgYGYBQ&usg=AFQjCNHjM9m__Hrumh-ecOsSE00-JkjKBQ&sig2=zDeSqOgs02AXJXj78
>w5I9g&bvm=bv.80642063,d.cGE&cad=rja
>[5]
>https://gist.githubusercontent.com/ryan-williams/8a162367c4dc157d2479/raw/
>4ab0bd6e76d9fc5745eb4b45cdf13195d10efaa2/mvn%20test,%20post%20clean,%20nee
>d%20dependencies%20built
>[6]
>https://gist.githubusercontent.com/ryan-williams/8a162367c4dc157d2479/raw/
>f4c7e6fc8c301f869b00598c7b541dac243fb51e/dev%20run-tests,%20post%20clean
>(50 mins)
>[7]
>https://gist.github.com/ryan-williams/57f8bfc9328447fc5b97#file-dev-run-te
>sts-failure-too-many-files-open-then-hang-L5260
>(1hr)
>[8] https://gist.github.com/ryan-williams/d0164194ad5de03f6e3f (1hr)
>[9] https://issues.apache.org/jira/browse/SPARK-3867
>[10] https://gist.github.com/ryan-williams/735adf543124c99647cc
>[11] https://gist.github.com/ryan-williams/8d149bbcd0c6689ad564
>[12]
>https://gist.github.com/ryan-williams/07df5c583c9481fe1c14#file-gistfile1-
>txt-L853
>(~90 mins)
>[13]
>https://gist.github.com/ryan-williams/718f6324af358819b496#file-gistfile1-
>txt-L852
>(91 mins)
>[14]
>https://gist.github.com/ryan-williams/c06c1f4aa0b16f160965#file-gistfile1-
>txt-L854
>[15] https://gist.github.com/ryan-williams/f8d410b5b9f082039c73
>[16] https://gist.github.com/ryan-williams/2e94f55c9287938cf745
>[17]
>http://apache-spark-user-list.1001560.n3.nabble.com/quot-Too-many-open-fil
>es-quot-exception-on-reduceByKey-td2462.html
>[18]
>http://stackoverflow.com/questions/25707629/why-does-spark-job-fail-with-t
>oo-many-open-files
>[19] https://issues.apache.org/jira/browse/SPARK-4002
>[20] https://issues.apache.org/jira/browse/SPARK-4542
>[21]
>https://spark.apache.org/docs/latest/building-with-maven.html#spark-tests-
>in-maven
>[22] https://www.mail-archive.com/dev@spark.apache.org/msg06443.html
>[23]
>http://mail-archives.apache.org/mod_mbox/spark-dev/201410.mbox/%3CCAOhmDze
>UNhuCr41B7KRPTEwMn4cga_2TNpZrWqQB8REekokxzg@mail.gmail.com%3E

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