[jira] [Commented] (CASSANDRA-15803) Separate out allow filtering scanning through a partition versus scanning over the table

["Stefan Miklosovic (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-15803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17715736#comment-17715736 ] 

Stefan Miklosovic commented on CASSANDRA-15803:
-----------------------------------------------

the patch for not failing when ALLOW FILTERING is not used for cases when all primary keys are specified is here 

https://github.com/apache/cassandra/pull/2293/files

So it solve this, until now, this would fail but it does not anymore.

{code}
create table ks.tb (id int, cl1 int, cl2 int, col1 int, primary key ((id), cl1, cl2))
select * from ks2.tb where id = 1 and cl1 = 2 and cl2 = 3 and col1 = 4;
{code}

This is something different from ALLOW FILTERING [WITHIN PARTITION]. What my patch fixes is the case when we are selecting on fully enumerated primary key.  There is no reason to require ALLOW FILTERING whatsoever if we _know_ that we are hitting one row only.

WITHIN PARTITION means that we _know_ that our query is looking into multiple rows in one partition. WITHIN PARTITION might be used for cases like this:

{code}
create table ks.tb (id int, cl1 int, cl2 int, col1 int, primary key ((id), cl1, cl2))
select * from ks2.tb where id = 1 and cl1 = 2 and col1 = 3 ALLOW FILTERING WITHIN PARTITION;
{code}

This is not done yet. I would try to solve it all in this ticket. I created CASSANDRA-18477 but I realized that it is basically a duplicate and it is better if this will be all fix in one shot.

> Separate out allow filtering scanning through a partition versus scanning over the table
> ----------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-15803
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15803
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: CQL/Syntax
>            Reporter: Jeremy Hanna
>            Priority: Normal
>
> Currently allow filtering can mean two things in the spirit of "avoid operations that don't seek to a specific row or sequential rows of data."  First, it can mean scanning across the entire table to meet the criteria of the query.  That's almost always a bad thing and should be discouraged or disabled (see CASSANDRA-8303).  Second, it can mean filtering within a specific partition.  For example, in a query you could specify the full partition key and if you specify a criterion on a non-key field, it requires allow filtering.
> The second reason to require allow filtering is significantly less work to scan through a partition.  It is still extra work over seeking to a specific row and getting N sequential rows though.  So while an application developer and/or operator needs to be cautious about this second type, it's not necessarily a bad thing, depending on the table and the use case.
> I propose that we separate the way to specify allow filtering across an entire table from specifying allow filtering across a partition in a backwards compatible way.  One idea that was brought up in Slack in the cassandra-dev room was to have allow filtering mean the superset - scanning across the table.  Then if you want to specify that you *only* want to scan within a partition you would use something like
> {{ALLOW FILTERING [WITHIN PARTITION]}}
> So it will succeed if you specify non-key criteria within a single partition, but fail with a message to say it requires the full allow filtering.  This would allow for a backwards compatible full allow filtering while allowing a user to specify that they want to just scan within a partition, but error out if trying to scan a full table.
> This is potentially also related to the capability limitation framework by which operators could more granularly specify what features are allowed or disallowed per user, discussed in CASSANDRA-8303.  This way an operator could disallow the more general allow filtering while allowing the partition scan (or disallow them both at their discretion).



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