Deadlock accessing SYS.SYSSTATISTICS
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Key: DERBY-4881
URL: https://issues.apache.org/jira/browse/DERBY-4881
Project: Derby
Issue Type: Bug
Components: SQL
Affects Versions: 10.6.2.1, 10.5.3.0, 10.4.2.0, 10.3.3.0, 10.7.1.0
Reporter: Kristian Waagan
Assignee: Kristian Waagan
Priority: Minor
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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