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From "Mike Matrigali (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5493) Same value returned by successive calls to a sequence generator.
Date Thu, 12 Apr 2012 17:29:19 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252625#comment-13252625
] 

Mike Matrigali commented on DERBY-5493:
---------------------------------------

rick, should I move forward and fix DERBY-5494 separate from the patch in this issue?  I have
been spending time looking at it rather than reviewing this change? I think i can code rest
of that fix today and if tests pass tonight be ready to checkin tommorow.

 I think both my proposed fix and your patch (by using a user level transaction) are both
causing the log to be flushed to avoid the crash problem.  For sequences I assume this is
necessary and we will have to pay the perfomance cost.  I don't think there is anyway to solve
the crash problem without forcing the log at commit time of the system catalog update.
                
> Same value returned by successive calls to a sequence generator.
> ----------------------------------------------------------------
>
>                 Key: DERBY-5493
>                 URL: https://issues.apache.org/jira/browse/DERBY-5493
>             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, 10.9.0.0
>            Reporter: Rick Hillegas
>            Assignee: Rick Hillegas
>              Labels: derby_triage10_9
>         Attachments: derby-5493-01-aa-correctnessPlusPeekerPlusTest.diff, derby-5493-01-ad-simplerApproach.diff,
derby-5493-01-ae-simplerApproachWithCrashJUnitTest.diff
>
>
> The following script shows the same value being returned from a sequence generator by
two successive NEXT VALUE FOR calls. Thanks to Knut for finding this:
> connect 'jdbc:derby:memory:db;create=true';
> create table t (x int);
> create sequence s;
> autocommit off;
> select count(*) from sys.syssequences with rs;
> values next value for s;
> drop table t;
> rollback;
> -- same value as previous call
> values next value for s; 

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