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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5151) Don't leak unused identity/sequence values on abnormal exit.
Date Tue, 06 Sep 2011 14:05:11 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5151?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13098014#comment-13098014

Rick Hillegas commented on DERBY-5151:

Hi Kristian. Work on DERBY-4437 fixed a related problem: now we don't leak identity/sequence
values on normal exit. And work on that issue makes it possible to set the length of the preallocated
range to 1, which will stop Derby from leaking identity/sequence values at the cost of reducing
scalability. However, if you want good scalability then you have to tolerate leaking identity/sequence
values on abnormal exit. So it seems to me that this issue is still alive. Thanks-Rick

> Don't leak unused identity/sequence values on abnormal exit.
> ------------------------------------------------------------
>                 Key: DERBY-5151
>                 URL: https://issues.apache.org/jira/browse/DERBY-5151
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Mark Holster
>         Attachments: sequence-no-cache.patch
> Currently, a sequence in Derby always uses a pre allocating cache. I'm working on an
usecase which requires a number to increase with a fixed value. The usecase fails after a
restart because of the pre allocating cache.
> I've created a patch that adds the options CACHE | NO CACHE to the create sequence statement.
When no cache is provided, the pre allocating cache size will be set to 1, which results in
a "no cache sequence".
> I've followed the CYCLE | NO CYCLE code as much as possible. Tested it in my own app
and it seems to work fine.
> RH: Note that part of this issue has been addressed by the work on DERBY-4437. Sequence
values will NOT leak now if you perform an orderly shutdown of your database. However, values
still leak if the VM exits before the database has been shutdown. I have changed this issue's
title to indicate that the remaining work applies to both sequences and identity columns.

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