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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4422) Extremely slow subqueries when subquerying on strings
Date Fri, 23 Oct 2009 21:22:00 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12769457#action_12769457
] 

Knut Anders Hatlen commented on DERBY-4422:
-------------------------------------------

The procedure should be there in version 10.5.3.0, but your database was probably created
with an earlier version of Derby and hasn't been upgraded to the new database format yet,
I'd guess. For the purpose of this experiment, the following statements should have the same
effect and refresh the index statistics:

  CALL SYSCS_UTIL.SYSCS_COMPRESS_TABLE('BLAH', 'OC_CONCEPTS', 1);
  CALL SYSCS_UTIL.SYSCS_COMPRESS_TABLE('BLAH', 'OC_CONCEPT_STRINGS', 1);

> Extremely slow subqueries when subquerying on strings
> -----------------------------------------------------
>
>                 Key: DERBY-4422
>                 URL: https://issues.apache.org/jira/browse/DERBY-4422
>             Project: Derby
>          Issue Type: Bug
>    Affects Versions: 10.5.3.0
>         Environment: Suse Unix 10.3.
>            Reporter: Tony Brusseau
>         Attachments: tmp2.sql
>
>
> SELECT DISTINCT C.INTERNAL_ID 
> FROM OC_CONCEPTS C
> WHERE
>    (C.INTERNAL_ID IN (SELECT DISTINCT OCS.CONCEPT_ID FROM OC_CONCEPT_STRINGS OCS WHERE
OCS.CONCEPT_ID=1))
> Both queries above are trivial and they are both acting on fully indexed primary key
columns. This query runs just fine. 
> However, when I make the small modification of searching on an indexed text column in
the sub query, it takes over 6 seconds to run, even though both queries independently take
< 1ms run.
> SELECT DISTINCT C.INTERNAL_ID 
> FROM OC_CONCEPTS C
> WHERE
>    (C.INTERNAL_ID IN (SELECT DISTINCT OCS.CONCEPT_ID FROM OC_CONCEPT_STRINGS OCS WHERE
OCS.NL_LC = 'dash'))

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