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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 Fri, 13 Apr 2012 14:22:18 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13253404#comment-13253404
] 

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

Thanks for that warning about the write-cache on Mac OSX, Mike. I believe that the write-cache
is enabled by default, so that would account for the high transaction rate.

I have run a similar experiment on a beefier machine (32 processor, Solaris). The transaction
rate is in the range which you would expect for a disabled write-cache. This experiment ran
32 threads:

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 32 \

I ran the experiment 3 times against the current trunk and then 3 times against the patch
(averaging the results). With the old sequence management (what's currently in the trunk),
I got 49 tx/sec.. With the patch, I got 75 tx/sec..

                
> 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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