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