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Posted to derby-dev@db.apache.org by "Rick Hillegas (JIRA)" <ji...@apache.org> on 2014/05/01 21:15:15 UTC
[jira] [Updated] (DERBY-6542) Improve the concurrency of identity
columns by using SYS.SYSSEQUENCES
[ https://issues.apache.org/jira/browse/DERBY-6542?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Rick Hillegas updated DERBY-6542:
---------------------------------
Attachment: derby-6542-02-ac-useNewSequenceGenerator.diff
Attaching derby-6542-02-ac-useNewSequenceGenerator.diff. This is the patch after merging with the head of trunk in order to pick up the bug fixes in derby-6554-01-ad-bugfixes.diff.
This patch will not pass the regression tests cleanly because of DERBY-6554. We have regression tests which create a table with an identity column and then, in the same transaction, populate it. With sequence-backed identity columns, this gives rise to the DERBY-6554 bug.
> Improve the concurrency of identity columns by using SYS.SYSSEQUENCES
> ---------------------------------------------------------------------
>
> Key: DERBY-6542
> URL: https://issues.apache.org/jira/browse/DERBY-6542
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.11.0.0
> Reporter: Rick Hillegas
> Assignee: Rick Hillegas
> Attachments: derby-6542-01-ab-catalog.diff, derby-6542-02-ab-useNewSequenceGenerator.diff, derby-6542-02-ac-useNewSequenceGenerator.diff
>
>
> This is another attempt to improve the concurrency of identity columns. The previous attempt was tracked by DERBY-4437.
> This new attempt will try out Mike's last suggestion: use system-created sequences managed by SYS.SYSSEQUENCES. This should reduce the contention on the core catalogs.
> I'm hopeful about this approach because of the experiments tracked by DERBY-6533. There we are not seeing any problems related to sequence generators but we are seeing lots of identity-related lock timeouts.
> Here is the general shape of this approach:
> 1) When adding an identity column to a table, Derby will create a sequence generator for the column. The sequence generator will live in the SYS schema and its name will be the table's UUID.
> 2) DROP SEQUENCE will not operate on system-created sequences. System-created sequences will be dropped/modified by DROP/ALTER TABLE commands.
> 3) We will add a new system function for inspecting the current, in-memory value of an identity generator without getting a lock on SYS.SYSSEQUENCES: SYSCS_UTIL.SYSCS_PEEK_AT_IDENTITY( tableSchemaName, tableName ).
> 4) Derby will create a sequence for every legacy identity column after hard-upgrade.
> 5) These changes will take place only after hard-upgrade. Soft-upgrade will not change the behavior of identity columns.
> Comments on this proposal are welcome. Thanks.
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