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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5494) Same value returned by successive calls to a sequence generator flanking an unorderly shutdown.
Date Thu, 07 Jun 2012 21:40:23 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13291327#comment-13291327

Mike Matrigali commented on DERBY-5494:

The perfomance results posted are along what I expect given the work gone into 10.9.  Default
behavior seems better or same for both
identity and sequences.

The preallocation of 1, single user sequence is the worst case I can think of.  In order to
insure that a sequence number is not given out
twice a synchonous commit is done for each allocation, where it was asynchronous in 10.8.
 Not sure if we should document the 
50 fold slowdown in the worst case.  If user does not touch tuning knobs we expect no slow
down, and on this platform see a slight
performance gain.
> 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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