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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4849) Re-compilation may cause duplicate entries in the XPLAIN table
Date Mon, 01 Nov 2010 19:40:27 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4849?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12927105#action_12927105
] 

Knut Anders Hatlen commented on DERBY-4849:
-------------------------------------------

I'm wondering if it would make sense to change the isolation level in the code that reads
SYSSTATISTICS to read uncommitted. I cannot see any harm in the optimizer reading statistics
that haven't been committed yet, and I think it would prevent deadlocks like the ones we see
in this test.

> 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, 10.7.1.0
>            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-4849-2c-broad_fix_with_test.diff, 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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