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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5691) Document that Write Caching must be disabled to avoid possible database corruption
Date Tue, 08 May 2012 16:27:48 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13270579#comment-13270579
] 

Mike Matrigali commented on DERBY-5691:
---------------------------------------

with respect to compressed file systems I don't think we ever verified a problem.  At one
point we saw some corruptions on compressed file system and out of disk space but never could
reproduce.   I don't think we ever test this configuration.  The concern is that derby only
expects an out of disk space error when growing the file.  The concern was that we would write
a mostly 0 filled page at alloc time and succeed. Then fill up the disk.  Then do something
to the page that would require the compressed version of the page to take more space and failing
at that point.   The system is not designed
to handle this.  Again this is all a theory as there has been no repro or testing, and would
be particular to what kind of
compression is being done.

One particularly bad case would be if only half of an updated page gets written before out
of disk space we are likely to get unrecoverable checksum errors. 
                
> Document that  Write Caching  must be disabled to avoid possible database corruption
> ------------------------------------------------------------------------------------
>
>                 Key: DERBY-5691
>                 URL: https://issues.apache.org/jira/browse/DERBY-5691
>             Project: Derby
>          Issue Type: Improvement
>          Components: Documentation
>         Environment: Microsoft Windows
>            Reporter: Stan Bradbury
>            Assignee: Kim Haase
>              Labels: Write_caching
>         Attachments: DERBY-5691-2.diff, DERBY-5691-2.stat, DERBY-5691-2.zip, DERBY-5691-3.diff,
DERBY-5691-3.zip, DERBY-5691.diff, DERBY-5691.stat, DERBY-5691.zip
>
>
> Suggestion that we document a recommendation that Windows Write Caching be disabled on
machines using Derby.
> The following article warns about Write Caching on Windows as a possbile source of database
corruption:
>      http://support.microsoft.com/kb/281672
> It is possible that this could be the cause of some unexplained Derby corruptions identified
after power failure of other system interupt.
> Links explaining how to disable Write Caching:
>   Win 2K: http://support.microsoft.com/kb/259716
>    Win 2008: http://support.microsoft.com/kb/324805
> From the Windows 2008 article:
> With some third-party programs, disk write caching has to be turned on or off. Additionally,
turning disk write caching on may increase operating system performance; however, it may also
result in the loss of information if a power failure, equipment failure, or software failure
occurs. This article describes how to turn disk write caching on or off.

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