Re: WAL documentation changes

Bruce,

In your document change which one can be placed on non-journalling
file system? data? wal? or both?

For me it seems it's not clear.
--
Tatsuo Ishii
SRA OSS, Inc. Japan

> Josh Berkus wrote:
> > 
> > >> First, none of the general purpose filesystems I've seen so far do data
> > >> journalling per default, since it's a huge performance penalty, even for
> > >> non-RDBMS workloads. The feature you talk about is ext3 specific (and
> > >> should be pointed out as such) and only disables write ordering, meaning
> > >> that metadata and file content updates are not synchronized.
> > > 
> > > You are right that my docs were misleading.  I have improved them by
> > > mentioning that it is _data_ flush that as part of journalling that can
> > > be a problem, and documented that the mount option listed is
> > > ext3-specific, not linux-specific.
> > 
> > Actually, I think that some of the other journalling filesystems allow 
> > data journalling (I know ReiserFS does), they just don't default to it. 
> >   For that matter, a few (ZFS in particular) have data journalling which 
> > can't be turned off.  While it's not a tuning parameter, users should be 
> > warned that they'll take a performance hit from it.
> 
> So I assume you are saying the docs are fine now.
> 
> -- 
>   Bruce Momjian  <bruce@momjian.us>        http://momjian.us
>   EnterpriseDB                             http://enterprisedb.com
> 
>   + If your life is a hard drive, Christ can be your backup. +
> 
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