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Date: Tue, 27 Oct 2009 16:42:59 +0000 (UTC)
From: "Tony Brusseau (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-4422) Extremely slow subqueries when
 subquerying on strings
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    [ https://issues.apache.org/jira/browse/DERBY-4422?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12770560#action_12770560 ] 

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

Yeah the query plans that I added were for the real query that I'm trying to optimize. 

SELECT DISTINCT C.EXTERNAL_ID, C.OWL_NL_ID, CYCL, C.PREFERRED_NL,
   C.PREFERRED_NL_SORTABLE, C.COMMENT, C.CONCEPT_TYPE, CS.NL, CS.STRING_TYPE,
   C.INTERNAL_ID FROM OC_CONCEPTS C, OC_CONCEPT_STRINGS CS
WHERE
   (C.INTERNAL_ID IN (SELECT DISTINCT OCS.CONCEPT_ID FROM OC_CONCEPT_STRINGS OCS WHERE OCS.NL_LC like 'dash%'))
   AND
   (C.INTERNAL_ID = CS.CONCEPT_ID)
ORDER BY C.PREFERRED_NL_SORTABLE, C.INTERNAL_ID, CS.STRING_TYPE

I'll add query plans for the queries I mentioned in the original report (which are simplifications of this query) in a bit.


> 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: fixed-time-derby.log, 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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