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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 Thu, 12 Apr 2012 16:13:21 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252528#comment-13252528
] 

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

derby-5494_diff_1a.txt passed all tests, still more work needed for checkin. Note that this
fix will decrease the performance of using sequences. The amount of the affect depends on
how many "block" updates done per measured benchmark, and if the benchmark must wait on those
updates. I think the worst case would be a single user insert benchmark that rarely commits,
using one or more next sequence calls per inserted row. Large numbers of inserts per transaction
is the usual case we recommend for users that want to insert as fast as possbile. I have not
done the measurement recently but it use to be not unusual that you had to do > 10000 inserts
per transaction to max out cpu on a single processor or you would just get I/O bottlenecked
on the commit record. Make sure to measure on a machine that has proper disk syncing. After
this fix each block update will have to wait for an I/O to hit disk at commit time. 

                
> 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
>         Attachments: derby-5494_diff_1a.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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