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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-1704) Allow more concurrency in the lock manager
Date Fri, 19 Jan 2007 14:09:30 GMT

    [ https://issues.apache.org/jira/browse/DERBY-1704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12466055
] 

Knut Anders Hatlen commented on DERBY-1704:
-------------------------------------------

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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