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https://issues.apache.org/jira/browse/CASSANDRA-12915?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15897393#comment-15897393
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Alex Petrov commented on CASSANDRA-12915:
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Thank you very much for the patch, I have a couple of questions:
*
[here|https://github.com/iksaif/cassandra/commit/4c8981a9b900a38dd67b3bb1560aaac7cc7ccfac#diff-88eaa3c77aa17a84006ad76f3151ed31L162],
as far as I understand the code (and purpose), adding an empty range to
current range doesn't change the range, why do you think we should remove
{{ranges.isEmpty()}}?
* when comparing range sizes, there's a check for emptiness which looks
redundant, for example
[here|https://github.com/iksaif/cassandra/commit/4c8981a9b900a38dd67b3bb1560aaac7cc7ccfac#diff-88eaa3c77aa17a84006ad76f3151ed31R294]
and
[here|https://github.com/iksaif/cassandra/commit/4c8981a9b900a38dd67b3bb1560aaac7cc7ccfac#diff-88eaa3c77aa17a84006ad76f3151ed31R301]
also,
[here|https://github.com/iksaif/cassandra/commit/4c8981a9b900a38dd67b3bb1560aaac7cc7ccfac#diff-88eaa3c77aa17a84006ad76f3151ed31R255].
In other words, there's nothing special about empty ranges. We can just return
an empty range instead of null and that's pretty much it.
> 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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