Re: Controlling Load Distributed Checkpoints

On Thu, Jun 07, 2007 at 10:16:25AM -0400, Tom Lane wrote:
> Heikki Linnakangas <heikki@enterprisedb.com> writes:
> > Thinking about this whole idea a bit more, it occured to me that the 
> > current approach to write all, then fsync all is really a historical 
> > artifact of the fact that we used to use the system-wide sync call 
> > instead of fsyncs to flush the pages to disk. That might not be the best 
> > way to do things in the new load-distributed-checkpoint world.
> 
> > How about interleaving the writes with the fsyncs?
> 
> I don't think it's a historical artifact at all: it's a valid reflection
> of the fact that we don't know enough about disk layout to do low-level
> I/O scheduling.  Issuing more fsyncs than necessary will do little
> except guarantee a less-than-optimal scheduling of the writes.

If we extended relations by more than 8k at a time, we would know a lot
more about disk layout, at least on filesystems with a decent amount of
free space.
-- 
Jim Nasby                                      decibel@decibel.org
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)