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https://issues.apache.org/jira/browse/DERBY-5494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13291761#comment-13291761
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Rick Hillegas commented on DERBY-5494:
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I would be happy to build a new release candidate if we wanted to add a release
note explaining how to get better concurrency for sequences by adjusting the
value of derby.language.sequence.preallocator.
Note, however, that the derby.language.sequence.preallocator knob is added by
10.9. It does not appear in 10.8. The knob was added by
derby-4437-05-aa-pluggablePreallocation.diff (revision 1138434), ported to 10.8
by revision 1141645, but backed out of 10.8 by
derby-5448-01-aa-backoutConcurrencyChanges.diff (revision 1179717).
So I would not expect that this knob would be set by users upgrading from 10.8.
Users upgrading from 10.8 will get the new default preallocation size of 100.
Mamta and I have run experiments with different settings of
derby.language.sequence.preallocator. So far our only evidence is that the
concurrency of sequences is better in 10.9 than in 10.8.
At this point, I don't know what a release note would say other than "We expect
that the concurrency of your sequence generators has gone up by upgrading to
10.9. If you want even better concurrency, consider adjusting
derby.language.sequence.preallocator."
Does that advice merit a release note? Is there some other advice we should
give in a release note? Does this advice merit a new release candidate?
Thanks,
-Rick
> Same value returned by successive calls to a sequence generator flanking an
> unorderly shutdown.
> -----------------------------------------------------------------------------------------------
>
> Key: DERBY-5494
> URL: https://issues.apache.org/jira/browse/DERBY-5494
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.6.1.0, 10.6.2.1, 10.7.1.1, 10.8.1.2, 10.8.2.2,
> 10.9.1.0
> Reporter: Rick Hillegas
> Assignee: Mike Matrigali
> Labels: derby_backport_reject_10_8, derby_triage10_9
> Fix For: 10.9.1.0, 10.10.0.0
>
> Attachments: derby-5494_3.diff, derby-5494_diff_1a.txt,
> derby-5494_diff_2.txt
>
>
> The following sequence of steps causes a sequence generator to return the
> same value on successive NEXT VALUE FOR calls.
> 1) Bring up ij and issue the following commands:
> connect 'jdbc:derby:db;create=true';
> create sequence s;
> values next value for s;
> 2) Control-c out of ij so that the engine comes down hard without an orderly
> shutdown.
> 3) Now bring up ij again and issue the following commands:
> connect 'jdbc:derby:db';
> values next value for s;
> Thanks to Knut for finding this one.
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