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From "Vladimir Ozerov (JIRA)" <j...@apache.org>
Subject [jira] [Closed] (IGNITE-6085) SQL: JOIN with multiple conditions is extremely slow
Date Mon, 06 May 2019 12:27:00 GMT

     [ https://issues.apache.org/jira/browse/IGNITE-6085?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Vladimir Ozerov closed IGNITE-6085.
-----------------------------------

> 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
>            Priority: Major
>              Labels: performance
>
> 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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