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https://issues.apache.org/jira/browse/DERBY-6542?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Rick Hillegas updated DERBY-6542:
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Attachment: derby-6542-02-af-useNewSequenceGenerator.diff
Attaching derby-6542-02-af-useNewSequenceGenerator.diff. This syncs the
previous rev of the patch with the work done on DERBY-6554 and implements the
correct ALTER TABLE behavior described on DERBY-6579. I am running tests now.
Touches the following additional files:
M
java/testing/org/apache/derbyTesting/functionTests/tests/lang/AlterTableTest.java
M
java/testing/org/apache/derbyTesting/functionTests/tests/lang/AutoIncrementTest.java
> 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,
> derby-6542-02-af-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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