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From "Mikkel Kamstrup Erlandsen (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-4007) Optimization of IN with nested SELECT
Date Tue, 13 Jan 2009 15:05:00 GMT

     [ https://issues.apache.org/jira/browse/DERBY-4007?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Mikkel Kamstrup Erlandsen updated DERBY-4007:

    Attachment: dblook_p_index.log

The dblook dump for the database with the PC ((parentId,childId) on summa_relations) index
dropped and replaced by a non-unique index P om parentId only.

In this setup the query still takes about 20-30s to complete.

> Optimization of IN with nested SELECT
> -------------------------------------
>                 Key: DERBY-4007
>                 URL: https://issues.apache.org/jira/browse/DERBY-4007
>             Project: Derby
>          Issue Type: Bug
>          Components: Performance
>    Affects Versions:
>         Environment: Linux
>            Reporter: Mikkel Kamstrup Erlandsen
>            Priority: Minor
>         Attachments: dblook.log, dblook_p_index.log, derby.log, derby_p_index.log
> The problem is with the following query:
> UPDATE summa_records SET base='foobar' WHERE id IN ( SELECT parentId FROM summa_relations
WHERE childId='horizon_2615441');
> It takes in the order of 30s to run when we expect something in the order of 1-2ms.
> We have a setup with two tables
> summa_records:  1,5M rows
> summa_relations: ~350000 rows
> summa_records have and 'id' column that is also indexed and is the primary key. The summa_relations
table holds mappings between different ids.
> In our case the nested SELECT produces 2 hits, say, 'foo' and 'bar'. So the UPDATE on
these two hits should be quite snappy. If we run the SELECT alone it runs in an instant, and
also if we run with hardcoded ids for the IN clause:
> UPDATE summa_records SET base='foobar' WHERE id IN ('foo', 'bar');
> We have instant execution. I'll attach a query plan in a sec.

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