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