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https://issues.apache.org/jira/browse/DERBY-4881?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kristian Waagan closed DERBY-4881.
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Closing issue.
> 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: 10.3.3.0, 10.4.2.0, 10.5.3.0, 10.6.2.1, 10.7.1.1
> Reporter: Kristian Waagan
> Assignee: Kristian Waagan
> Priority: Minor
> Fix For: 10.6.2.3, 10.7.1.1
>
> 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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