Pawel Veselov created OPENJPA-2905:
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Summary: Sequences are altered unnecessarily
Key: OPENJPA-2905
URL: https://issues.apache.org/jira/browse/OPENJPA-2905
Project: OpenJPA
Issue Type: Bug
Components: jdbc
Affects Versions: 3.2.2, 3.2.1, 3.2.0, 3.1.2, 3.1.1, 3.1.0
Reporter: Pawel Veselov
{{NativeJDBCSeq.allocateInternal()}} attempts to alter a sequence for every
sequence encountered at least once during a runtime.
In Postgres, for example, executing this DDL requires that no other locks are
held, we are seeing this blockage:
{noformat}
blocked_pid | 12519
blocked_user | snapstore
blocking_pid | 29611
blocking_user | snapstore
blocked_statement | ALTER SEQUENCE campaign_seq INCREMENT
BY 50
current_statement_in_blocking_process | select id from other_lock where id = $1
for share
{noformat}
It doesn't make sense to alter the sequence if the sequence already has the
right increment, otherwise there are the following issues:
1. In a cluster, the alterations are going to be attempted by each node
2. If there is a sudden request, in the middle of operations, to get a sequence
value for some rarely written to table, that sequence can be held up for a long
time, unwarranted so, at least in Progress
I really recommend that the sequence increment is first checked, and is only
changed if it doesn't match the expectation, at least on the databases where
this is possible.
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