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From "Alex Petrov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12915) SASI: Index intersection can be very inefficient
Date Thu, 24 Nov 2016 14:27:58 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15693413#comment-15693413
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Alex Petrov commented on CASSANDRA-12915:
-----------------------------------------

bq. For the primary expression, AFAIK this code has always been dead

It might have been. But it still has some potential value, so it's better to fix it than to
just discard. Nothing is perfect. 

bq. estimated number of tokens 

This one is going to be harder without reading token trees. I mostly meant that we take first
idea from {{term}} count. With {{termSize}} just be careful since there might be variable-size
tokens. But we could put together a rough patch and benchmark it to see if that's a good direction...

> SASI: Index intersection can be very inefficient
> ------------------------------------------------
>
>                 Key: CASSANDRA-12915
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12915
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: sasi
>            Reporter: Corentin Chary
>             Fix For: 3.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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