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https://issues.apache.org/jira/browse/DERBY-5493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13251176#comment-13251176
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Mike Matrigali commented on DERBY-5493:
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I will review these changes more carefully in next few days, this comment is
just based on your comment describing the changes. Did you
understand why this approach fixes DERBY-5494 vs the subtransaction approach?
In the normal sub transaction case I was thinking
that it should wait on locks and return too much contention on a lock timeout,
to take care of a expected very short lock waits
if 2 threads are trying to update the sequence at same time, but maybe the 1
transaction per sequence makes this impossible to happen.
What is the expected behavior of creating a sequence, with respect to
autocommit and locking? Is the create done in the nested transaction
and autocommitted?
A comment I meant to make before, is that DERBY-5495 requires crash testing,
and now there is a framework to do that in junit tests -
see store/OCRecoveryTest.java, basically there is a routine to fork out a
process to run a java test procedure and then you just exit which
will run through the "unclean" shutdown and next test connects running through
whatever recovery will do on that unclean shutdown.
> 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
>
>
> 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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