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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4963) Revert to FileDescriptor#sync from FileChannel#force to improve interrupt resilience
Date Tue, 01 Mar 2011 21:17:03 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13001117#comment-13001117

Knut Anders Hatlen commented on DERBY-4963:

Thanks for writing the release note, Rick. It is clear and looks correct for the most part.
The one thing I believe is inaccurate, is the sentence "Solaris/JDK5 is one of these platforms."
I don't think Solaris is affected by this change, at least not on JDK 5.

I think the only platforms affected are those that suffered from DERBY-1, which are some old
releases of Java 1.4.2 and Java 5 on Mac OS/X and FreeBSD (and possibly other BSDs). And,
looking at the code, it probably also affects a code path taken by all JVMs at version 1.4.0
and 1.4.1, but I'm not sure if we still support those variants of 1.4 or if we require 1.4.2

Dag, does that sound correct, or did I garble things?

> Revert to FileDescriptor#sync from FileChannel#force to improve interrupt resilience
> ------------------------------------------------------------------------------------
>                 Key: DERBY-4963
>                 URL: https://issues.apache.org/jira/browse/DERBY-4963
>             Project: Derby
>          Issue Type: Improvement
>          Components: Store
>            Reporter: Dag H. Wanvik
>            Assignee: Dag H. Wanvik
>             Fix For:
>         Attachments: derby-4963-1.diff, derby-4963-1.stat, derby-4963-2.diff, derby-4963-2.stat,
> FileChannel.force is interruptable, and we really don't want to be interrupted when we
flush the log file.  Happily, on most platforms, we use the "rws"/"rwd" file open mask which
makes the writes thjemselves synchronized, so no subsequent explicit file level sync is needed
> DirFile4#getRandowmAccessFile should use plain DirRandomAccessFile instead of the current
DirRandomAccessFile4. This will make StorageRandomAccessFile#sync map to FileDescriptor#sync
instead of FileChannel#force (also for NIO supporting platforms). 
> Since FileDescriptor#sync does not allow synching file data only (it also synchronizes
metadata), those platforms which do not support write synchronization will experience a performance
drop, but this is the price we have to pay to survive interrupts without shutting down the
database on those platforms. 
> Users which experience this as a problem, should update to a newer JVM which does support
"rws"/"rwd" in the mode argument to java.io.RandomAccessFile (http://download.oracle.com/javase/6/docs/api/java/io/RandomAccessFile.html#RandomAccessFile(java.io.File,%20java.lang.String).
> Cf. also discussion on https://issues.apache.org/jira/browse/DERBY-4741?focusedCommentId=12977862&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#action_12977862

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