[jira] [Commented] (CASSANDRA-12915) SASI: Index intersection can be very inefficient

["Corentin Chary (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-12915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15682803#comment-15682803 ] 

Corentin Chary commented on CASSANDRA-12915:
--------------------------------------------

It looks like index that are returning no tokens at all are also completely ignored even when the operator is AND. In this case it would be simple to simply stop doing any work and return early with an empty result.

> SASI: Index intersection can be very inefficient
> ------------------------------------------------
>
>                 Key: CASSANDRA-12915
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12915
>             Project: Cassandra
>          Issue Type: Bug
>          Components: sasi
>            Reporter: Corentin Chary
>
> It looks like RangeIntersectionIterator.java and be pretty inefficient in some cases. Let's take the following query:
> SELECT data FROM table WHERE index1 = 'foo' AND index2 = 'bar';
> In this case:
> * index1 = 'foo' will match 2 items
> * index2 = 'bar' will match ~300k items
> On my setup, the query will take ~1 sec, most of the time being spent in disk.TokenTree.getTokenAt().
> if I patch RangeIntersectionIterator so that it doesn't try to do the intersection (and effectively only use 'index1') the query will run in a few tenth of milliseconds.
> I see multiple solutions for that:
> * Add a static thresold to avoid the use of the index for the intersection when we know it will be slow. Probably when the range size factor is very small and the range size is big.
> * CASSANDRA-10765



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