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From "Alex Petrov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12915) SASI: Index intersection with an empty range really inefficient
Date Wed, 08 Mar 2017 10:23:38 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15901028#comment-15901028
] 

Alex Petrov commented on CASSANDRA-12915:
-----------------------------------------

bq. I think it would be better not to make the assumption that null range == empty range.
Mostly because it isn't treated the same way in add()

Agree, fixed.

bq. That's not how intersection usually works

You're right. I was thinking to make it for both union and intersection cases. But since we
use it only in the intersection case, we can flip the "emptiness" logic and still remove the
check for empty. 

> SASI: Index intersection with an empty range really inefficient
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-12915
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12915
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: sasi
>            Reporter: Corentin Chary
>            Assignee: Corentin Chary
>             Fix For: 3.11.x, 4.x
>
>
> 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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