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From "Rick Hillegas (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-5493) Same value returned by successive calls to a sequence generator.
Date Tue, 17 Apr 2012 18:13:17 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5493?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Rick Hillegas updated DERBY-5493:
---------------------------------

    Attachment: derby-5493-01-af-usersubtran.diff

Attaching derby-5493-01-af-usersubtran.diff. This patch fixes the concurrency problems with
the previous patch which were disclosed by the experiments described on DERBY-5471.

The fix is to go back to updating SYSSEQUENCES in a subtransaction of the user's execution
transaction. This means that this patch does not fix DERBY-5494. So I won't commit this patch
until Mike commits his work on DERBY-5494. At that point, I will adjust the patch to account
for the fact that Mike is going to include the regression test case for that issue which was
introduced by the earlier rev of this patch.

With this version of the patch the tx/sec results are slightly better than the comparable
experiments on 10.8.2.2 and trunk:

o 10 threads with preallocation=20: 99 vs 92 on trunk

o 10 threads with preallocation=5: 78 vs 75 on 10.8.2.2

o 1 thread with preallocation=20: 45 vs 44 on trunk

o 1 thread with preallocation=5: 36 vs 35 on 10.8.2.2

                
> 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, derby-5493-01-af-usersubtran.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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