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From "Kathey Marsden (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5691) Document that Write Caching must be disabled to avoid possible database corruption
Date Thu, 26 Apr 2012 23:42:48 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13263257#comment-13263257
] 

Kathey Marsden commented on DERBY-5691:
---------------------------------------

Thank you Kim for adding this important documentation. 

Some specific corrections changes:

1)To provide an overview of the overall problem. I would say add a high level description
before "To avoid ... e.g.

Derby must be able to sync to disk. Some machine, disk or operating system  settings can prevent
a proper sync and cause unrecoverable database corruption on power failure system or software
crash.  To avoid database corruption, you can do the following.

2) I would add a sentence after: Do not enable disk write caching on the hard drive that holds
the database. 
Disable write caching if it is on by default.

3) Take out  "If possible," before run Derby on a local drive.

4)For runtime compression I was not referring to the stored procedures, but rather sometimes
there is an operating system setting that allows for runtime compression of the files. 

Maybe add a catch all. Disable any other options that might prevent a proper sync to disk
when Derby is writing its transaction logs or other data.

---

In general, it would be good in the developers guide to point to the maintaining integrity
doc  as when Derby is embedded in an application, it is really the embedding product and its
users that have to take on this role of maintaining database integrity. The embedding product
needs to incorporate backup/restore procedures and recommendations into their own product
documentation as well as these warnings.



                
> 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.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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