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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5494) Same value returned by successive calls to a sequence generator flanking an unorderly shutdown.
Date Fri, 08 Jun 2012 13:08:23 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13291761#comment-13291761

Rick Hillegas commented on DERBY-5494:

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?


> Same value returned by successive calls to a sequence generator flanking an unorderly
> -----------------------------------------------------------------------------------------------
>                 Key: DERBY-5494
>                 URL: https://issues.apache.org/jira/browse/DERBY-5494
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions:,,,,,
>            Reporter: Rick Hillegas
>            Assignee: Mike Matrigali
>              Labels: derby_backport_reject_10_8, derby_triage10_9
>             Fix For:,
>         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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