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From "Mark Holster (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5151) Sequence without cache
Date Fri, 25 Mar 2011 21:05:05 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5151?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13011418#comment-13011418
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Mark Holster commented on DERBY-5151:
-------------------------------------

I don't know if it is a better option, but maby it is possible to "shut down" the sequence
when the database is shut down? On shutdown the sequence should write the current memory value
back to disk (based on best effort?). 
- The advantage of this approach is that it is not necessary to introduce more sql or properties.

- The disadvantage is that there can be only one SequenceUpdater instance per sequence, or
a mechanism should be created to make sure the sequence cache with the highest fetched value
is written back to disk.

> Sequence without cache
> ----------------------
>
>                 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.

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