Re: Controlling Load Distributed Checkpoints

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.

I'm not proposing to issue any more fsyncs. I'm proposing to change the 
ordering so that instead of first writing all dirty buffers and then 
fsyncing all files, we'd write all buffers belonging to a file, fsync 
that file only, then write all buffers belonging to next file, fsync, 
and so forth.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com