Re: WAL documentation changes

>> 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.

--Josh