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Posted to issues@ignite.apache.org by "Vladimir Ozerov (JIRA)" <ji...@apache.org> on 2017/11/14 17:05:00 UTC
[jira] [Comment Edited] (IGNITE-6085) SQL: JOIN with multiple
conditions is extremely slow
[ https://issues.apache.org/jira/browse/IGNITE-6085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16247236#comment-16247236 ]
Vladimir Ozerov edited comment on IGNITE-6085 at 11/14/17 5:04 PM:
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See IGNITE-4150. Probably similar fix in H2 could be applied.
was (Author: vozerov):
See IGNITE-4150. Probably similar fix ti H2 could be applied.
> SQL: JOIN with multiple conditions is extremely slow
> ----------------------------------------------------
>
> Key: IGNITE-6085
> URL: https://issues.apache.org/jira/browse/IGNITE-6085
> Project: Ignite
> Issue Type: Task
> Components: sql
> Affects Versions: 2.1
> Reporter: Vladimir Ozerov
> Labels: performance
> Fix For: 2.4
>
>
> Consider the following query:
> {code}
> SELECT ... FROM A a
> INNER JOIN B b ON b.id = a.foreign_id1 OR b.id = a.foreign_id2
> {code}
> In this case H2 cannot use indexes on {{foreign_id1}} or {{foreign_id2}} columns and query execution takes extraordinary time. Known workaround for a problem is to apply multiple JOINs, e.g.:
> {code}
> SELECT ... FROM A a
> LEFT OUTER JOIN B b1 ON b1.id = a.foreign_id1
> LEFT OUTER JOIN B b2 ON b2.id = a.foreign_id2
> WHERE b1.id IS NOT NULL AND b2.id IS NOT NULL
> {code}
> On a single real-world scenario it improved exeution time by a factor of 500 (from 4s to 80ms).
> Something is terribly wrong here. Probably, H2 cannot perform necessary query re-write, or cannot understand how to use index. Let's find a way to fix that.
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