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From "Knut Anders Hatlen (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-5623) Loosen up synchronization in FileMonitor
Date Tue, 21 Feb 2012 10:19:34 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5623?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Knut Anders Hatlen updated DERBY-5623:

    Attachment: d5623-1.diff

Thanks for the patch, David. I had played with a similar patch myself (see the attached file,
d5623-1.diff). My patch differs a little from your patch:

- It preserves the synchronization in getDaemonThread(). Without synchronization in that method,
I saw occasional IllegalThreadStateExceptions when booting and shutting down databases concurrently
in many threads.

- It uses PrivilegedAction instead of PrivilegedExceptionAction for the actions that don't
throw checked exceptions, which made the exception handling simpler.

All the regression tests passed with this patch.

I also ran an application that booted 1000 databases in 20 threads on a machine with 8 cores,
and the patch seemed to speed it up by 3-4%. It was primarily the removal of synchronization
in getJVMProperty() that contributed to the speed-up.

Although the speed-up is modest (at least in my environment) the patches remove more lines
of code than they add, which is a good thing in itself.
> Loosen up synchronization in FileMonitor
> ----------------------------------------
>                 Key: DERBY-5623
>                 URL: https://issues.apache.org/jira/browse/DERBY-5623
>             Project: Derby
>          Issue Type: Improvement
>          Components: Services
>    Affects Versions:
>            Reporter: Knut Anders Hatlen
>         Attachments: d5623-1.diff, derby-diff.txt
> When opening a large number of databases in parallel, many threads get stuck for a long
time in FileMonitor, as reported in this thread on derby-user:
> http://mail-archives.apache.org/mod_mbox/db-derby-user/201202.mbox/%3CCAEQ8c00vx0yFrwWyjm%3Dt_Yd%2BuuKGOL%3DSgpYfQuYghOOPgdN8-w%40mail.gmail.com%3E
> The synchronization in FileMonitor is only needed because the monitor instance is also
used as a shared PrivilegedExceptionAction instance. Since all databases share one FileMonitor
instance, threads that access any of these methods are serialized. If each method created
its own PrivilegedAction or PrivilegedExceptionAction instance instead of using the monitor's
run() method, these methods wouldn't need synchronization.

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