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Date: Tue, 19 Oct 2010 09:35:27 -0400 (EDT)
From: "Kristian Waagan (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-4849) Re-compilation may cause duplicate
 entries in the XPLAIN table
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    [ https://issues.apache.org/jira/browse/DERBY-4849?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12922554#action_12922554 ] 

Kristian Waagan commented on DERBY-4849:
----------------------------------------

Lily,

I can't see any performance issues with this patch. Some of the code is only executed if there is an exception, and the extra if's are "hidden behind" an existing if-condition (which is mostly false). Let me know if you were thinking of something in particular.
As for the testing, it may seem as updating the statistics in a loop is good enough to trigger the invalidation just at the right spot. Of course, I can't do it only once due to the timing requirements, so I made the test run both the select and the invalidation code, in separate threads, in a loop for 10 seconds.

Thanks,

> Re-compilation may cause duplicate entries in the XPLAIN table
> --------------------------------------------------------------
>
>                 Key: DERBY-4849
>                 URL: https://issues.apache.org/jira/browse/DERBY-4849
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.6.2.1, 10.7.0.0
>            Reporter: Kristian Waagan
>            Assignee: Kristian Waagan
>            Priority: Minor
>         Attachments: derby-4849-1a-narrow_fix.diff, derby-4849-2a-broad_fix.diff, derby-4849-2b-broad_fix_with_test.diff, derby-4849-2b-broad_fix_with_test.stat, derby-4849-xplain_duplicate_stacktrace.txt
>
>
> If happening at the right moment, a re-compilation request may cause duplicate entries in the XPLAIN statement tables.
> I have only confirmed this for the SYSXPLAIN_STATEMENTS table, and I do not know if the other XPLAIN tables are affected.
> The error is highly intermittent, and so far I have only been able to trigger it when testing the automatic index statistics update prototype.
> See the attached stack-trace for some more details.

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