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Date: Wed, 14 Dec 2005 20:20:47 +0100 (CET)
From: "Daniel John Debrunner (JIRA)" <derby-dev@db.apache.org>
To: derby-dev@db.apache.org
Subject: [jira] Commented: (DERBY-733) Starvation in RAFContainer.readPage()
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    [ http://issues.apache.org/jira/browse/DERBY-733?page=comments#action_12360447 ] 

Daniel John Debrunner commented on DERBY-733:
---------------------------------------------

I wonder if we can use the existing lock manager, which provides predictable queueing behaviour on granting locks,
rather than add a new mechansm.

> Starvation in RAFContainer.readPage()
> -------------------------------------
>
>          Key: DERBY-733
>          URL: http://issues.apache.org/jira/browse/DERBY-733
>      Project: Derby
>         Type: Improvement
>   Components: Performance, Store
>     Versions: 10.2.0.0, 10.1.2.1, 10.1.3.0, 10.1.2.2
>  Environment: Solaris x86 and Linux with Sun JVM 1.5.0. Derby embedded and client/server.
>     Reporter: Knut Anders Hatlen
>     Assignee: Knut Anders Hatlen
>  Attachments: DERBY-733.diff
>
> When Derby is completely disk bound, threads might be starved in
> RAFContainer.readPage(). This is a real problem when multiple clients
> are repeatedly accessing one or a small number of large tables. In
> cases like this, I have observed very high maximum response times
> (several minutes in the worst cases) on simple transactions. The
> average response time is not affected by this.
> The starvation is caused by a synchronized block in
> RAFContainer.readPage():
>   synchronized (this) {
>       fileData.seek(pageOffset);
>       fileData.readFully(pageData, 0, pageSize);
>   }
> If many threads want to read pages from the same file, there will be a
> long queue of threads waiting for this monitor. Since the Java
> specification does not guarantee that threads waiting for monitors are
> treated fairly, some threads might have to wait for a long time before
> they get the monitor. (Usually, a couple of threads get full throughput
> while the others have to wait.)

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