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https://issues.apache.org/jira/browse/DERBY-1704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12466055
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Knut Anders Hatlen commented on DERBY-1704:
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Attached cleanup1.diff.
I observed that LockSet extends Hashtable, but all calls to Hashtable's methods
are already synchronized on the LockSet, so it could just as well use a
HashMap. The attached patch makes LockSet contain a HashMap instead of
extending Hashtable. I ran some tests with the DERBY-1961 test client
(single-record select on a dual-cpu machine, Solaris 10, Java SE 6) and saw ~2%
throughput improvement for a single client and from 15% to 25% improvement for
multiple (2-64) clients.
Derbyall and the JUnit tests passed on Solaris 10/Java SE 6. Reviews would be
appreciated.
> Allow more concurrency in the lock manager
> ------------------------------------------
>
> Key: DERBY-1704
> URL: https://issues.apache.org/jira/browse/DERBY-1704
> Project: Derby
> Issue Type: Improvement
> Components: Performance, Services
> Affects Versions: 10.2.1.6
> Reporter: Knut Anders Hatlen
> Assigned To: Knut Anders Hatlen
> Priority: Minor
> Attachments: 1cpu.png, 2cpu.png, 8cpu.png, cleanup1.diff,
> cleanup1.stat, split-hashtables.diff, split-hashtables.stat
>
>
> I have seen indications of severe monitor contention in SinglePool
> (the current lock manager) when multiple threads access a Derby
> database concurrently. When a thread wants to lock an object, it needs
> to obtain the monitor for both SinglePool and LockSet (both of them
> are global synchronization points). This leads to poor scalability.
> We should investigate how to allow more concurrency in the lock
> manager, and either extend SinglePool or implement a new manager.
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