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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Resolved: (DERBY-4881) Deadlock accessing SYS.SYSSTATISTICS
Date Fri, 05 Nov 2010 15:28:43 GMT

     [ https://issues.apache.org/jira/browse/DERBY-4881?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Kristian Waagan resolved DERBY-4881.

       Resolution: Fixed
    Fix Version/s:

Tests passed.

Backported to the 10.6 branch with revision 1031623.

> Deadlock accessing SYS.SYSSTATISTICS
> ------------------------------------
>                 Key: DERBY-4881
>                 URL: https://issues.apache.org/jira/browse/DERBY-4881
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions:,,,,
>            Reporter: Kristian Waagan
>            Assignee: Kristian Waagan
>            Priority: Minor
>             Fix For:,
>         Attachments: derby-4881-1a-deadlock_fix.diff, derby-4881-1b-deadlock_fix.diff
> Transactions accessing index statistics can deadlock if one of them inserts new entries
and the other selects from the system table. Inserts happens for instance when update of index
statistics are perform manually, or when a table is compressed (given that the table has indexes
and contains some rows). This issue may be more problematic when automatic update of index
statistics is implemented.
> Issue discovered when writing a regression tests for DERBY-4849, see discussion there.
The bug is timing dependent, but has been observed on a variety of JVMs and platform architectures.
> To sum up:
>   o using NO_WAIT + retry was suggested, but turned out to be an infeasible solution
>   o current approach is to allow using read uncommitted isolation level when accessing
statistics in the system table (take no locks)

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