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From "Mike Matrigali (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 19:03:18 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5493?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252741#comment-13252741
] 

Mike Matrigali commented on DERBY-5493:
---------------------------------------

ok, i will move forward on DERBY-5494.  I will not be changing behavior of identity columns.
 I think we should look at that as a separate issue, and see if standard is open to interpretation
for identity columns. If at all possible I would like to keep the performance optimization
currently used with identity columns.  I will add comments in the code to make it obvious
what is going on, rather than hidden in store as it is now.   With identity columns I believe
the problem is much less vs sequences, at least in normal application expectations.  It seems
reasonable to me for applications to not "remember" an identity column value until the inserting
transaction commits, or to just use it in same transaction that inserted and produced the
value making its use transactional .  I think the current behaviour never results in duplicate
identity column values being produced for use in a row.
                
> 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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