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From "Mike Matrigali (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5494) Same value returned by successive calls to a sequence generator flanking an unorderly shutdown.
Date Wed, 11 Apr 2012 20:27:17 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13251895#comment-13251895
] 

Mike Matrigali commented on DERBY-5494:
---------------------------------------

i am looking at the latest test case posted in comments.  Looking at log traces is seems like
update of catalog row does get done in a nested transaction, and commit record is written
to stream, but does not look like a force of the log is happening at that point.  Not sure
why not, yet.  For some internal/nested transactions this behavior is ok as rather get the
performance of a nosync commit and we don't really care as long as either all or none of the
transaction gets done.  The is the case with btree splits.  I think it also makes sense for
identity columns as the nested transaction only is important once some other transaction that
uses one of the value commits, which in turn will force this transaction.  

I don't think sequences should be using this optimization and thought that only would happen
if they called commitNoSync() which I did not see in the code.

                
> 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, 10.9.0.0
>            Reporter: Rick Hillegas
>              Labels: derby_triage10_9
>
> 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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