Re: Sorting writes during checkpoint

Greg Smith <gsmith(at)gregsmith(dot)com> writes:
> On Sun, 4 May 2008, Tom Lane wrote:
>> Well, I tried a pgbench test similar to that one --- on smaller hardware
>> than was reported, so it was a bit smaller test case, but it should have
>> given similar results.

> ... If
> you're not offloading to another device like that, the OS-level elevator
> sorting will handle sorting for you close enough to optimally that I doubt
> this will help much (and in fact may just get in the way).

Yeah. It bothers me a bit that the patch forces writes to be done "all
of file A in order, then all of file B in order, etc". We don't know
enough about the disk layout of the files to be sure that that's good.
(This might also mean that whether there is a win is going to be
platform and filesystem dependent ...)

>> Unless someone can volunteer to test sooner, I think we should drop this
>> item from the current commitfest queue.

> From the perspective of keeping the committer's plates clean, a reasonable
> system for this situation might be for you to bounce this into the
> rejected pile as "Returned for testing" immediately, to clearly remove it
> from the main queue. A reasonable expectation there is that you might
> consider it again during May if someone gets back with said testing
> results before the 'fest ends.

Right, that's in the ground rules for commitfests: if the submitter can
respond to complaints before the fest is over, we'll reconsider the
patch.

regards, tom lane