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From "Tony Brusseau (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4422) Extremely slow subqueries when subquerying on strings
Date Tue, 27 Oct 2009 21:14:59 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12770643#action_12770643
] 

Tony Brusseau commented on DERBY-4422:
--------------------------------------

When the problematic query is separated into 2 separate queries, each separate query runs
extremely fast:

(SELECT DISTINCT CONCEPT_ID FROM OC_CONCEPT_STRINGS WHERE NL_LC = 'dash')

SELECT DISTINCT INTERNAL_ID
FROM OC_CONCEPTS
WHERE
   (INTERNAL_ID IN (23146, 97675, 105192, 127143))

However, when asked in subquery form:

SELECT DISTINCT INTERNAL_ID
FROM OC_CONCEPTS
WHERE
   (INTERNAL_ID IN (SELECT DISTINCT CONCEPT_ID FROM OC_CONCEPT_STRINGS WHERE NL_LC = 'dash'))


the query takes over 6 seconds to run.


> 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: derby.log, fixed-time-derby.log, SQLFile1.sqlaa.gz, SQLFile1.sqlab.gz,
SQLFile2.sqlaa.gz, SQLFile2.sqlab.gz, SQLFile2.sqlac.gz, tmp2.sql, unlimited-time-derby.log
>
>
> 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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