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From "Corentin Chary (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12915) SASI: Index intersection with an empty range really inefficient
Date Mon, 06 Mar 2017 21:30:33 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15898148#comment-15898148
] 

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

Could you re-phrase the question ? I though I answered everything from [this comment|https://issues.apache.org/jira/browse/CASSANDRA-12915?focusedCommentId=15897393&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15897393]
but it looks like I didn't.

The idea of my approach is that I'm looking for this behavior:

{code}
builder = RangeIntersectionIterator.builder(strategy);
builder.add(new LongIterator(new long[] {}));
builder.add(new LongIterator(new long[] {1}));
range = builder.build();

Assert.assertEquals(0, range.getCount());
Assert.assertFalse(range.hasNext()); // (optimized though isOverlapping() returning false
{code}

In other words, adding an empty iterator to a RangeIntersectionIterator should make it empty
and there is a strong different between an empty and null iterator. I believe in your case
your empty iterator will just get ignored because you need to remove this check: https://github.com/ifesdjeen/cassandra/blob/78b1ff630536b0f48787ced74a66d702d13637ba/src/java/org/apache/cassandra/index/sasi/utils/RangeIterator.java#L151

> 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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