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From "Rick Hillegas (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5493) Same value returned by successive calls to a sequence generator.
Date Thu, 12 Apr 2012 18:51:17 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252725#comment-13252725
] 

Rick Hillegas commented on DERBY-5493:
--------------------------------------

I have run a quick concurrency test against the patch, using the test introduced on derby-4565:

java org.apache.derbyTesting.perf.clients.Runner \
    -driver org.apache.derby.jdbc.EmbeddedDriver \
    -init \
    -load seq_gen \
    -load_opts debugging=0,numberOfGenerators=1,tablesPerGenerator=0,insertsPerTransaction=100
\
    -gen b2b \
    -threads 10 \

On my dual-core Mac I'm getting slightly better numbers (average of 291 tx/seconds) than I
recorded for this test case on derby-4565. I don't think the improvement is due to this patch,
it is more likely due to the fact that I have a faster machine this time around. However,
it encourages me to think that the patch has not harmed the concurrency of sequence generators.
I'm looking for a beefier machine with more processors now.
                
> 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
>
>
> 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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