Re: Postgresql Performance on an HP DL385 and

On Tue, Aug 15, 2006 at 05:38:43PM -0400, mark(at)mark(dot)mielke(dot)cc wrote:
> I didn't know that the xlog segment only uses pre-allocated space. I
> ignore mtime/atime as they don't count as file system structure
> changes to me. It's updating a field in place. No change to the structure.
>
> With the pre-allocation knowledge, I agree with you. Not sure how I
> missed that in my reviewing of the archives... I did know it
> pre-allocated once upon a time... Hmm....

This is only valid if the pre-allocation is also fsync'd *and* fsync
ensures that both the metadata and file data are on disk. Anyone
actually checked that? :)

BTW, I did see some anecdotal evidence on one of the lists a while ago.
A PostgreSQL DBA had suggested doing a 'pull the power cord' test to the
other DBAs (all of which were responsible for different RDBMSes,
including a bunch of well known names). They all thought he was off his
rocker. Not too long after that, an unplanned power outage did occur,
and PostgreSQL was the only RDBMS that recovered every single database
without intervention.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461