[jira] Commented: (DERBY-1704) Allow more concurrency in the lock manager

["Knut Anders Hatlen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-1704?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12472585 ] 

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

The results shown in the attached graphs are not valid for trunk after the commit of the DERBY-2107 patch. The single-record select load that was used is more latch-intensive than lock-intensive, and when the latches no longer use the lock manager, the effect of splitting the hash tables in the lock manager is small, even with multiple CPUs. There still is a positive effect for more lock-intensive loads though (for instance scans).

Since there are two global synchronization points in the lock manager, I'll file subtasks so they can be discussed separately.

> 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, cleanup1.v2.diff, cleanup2.diff, cleanup3.diff, cleanup3.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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