Re: Sorting writes during checkpoint

Greg Smith <gsmith(at)gregsmith(dot)com> writes:
> On Sun, 4 May 2008, Tom Lane wrote:
>> However, I am completely unable to measure any performance improvement
>> from it. Given the possible risk of out-of-memory failures, I think the
>> patch should not be applied without some direct proof of performance
>> benefits, and I don't see any.

> Fair enough. There were some pgbench results attached to the original
> patch submission that gave me a good idea how to replicate the situation
> where there's some improvement.

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. I didn't see any improvement; if anything it was
a bit worse. So that's what got me concerned.

Of course it's notoriously hard to get consistent numbers out of pgbench
anyway, so I'd rather see some other test case ...

> I expect I can take a shot at quantifying
> that independantly near the end of this month if nobody else gets to it
> before then (I'm stuck sorting out a number of OS level issue right now
> before my testing system is online again). Was planning to take a longer
> look at Greg Stark's prefetching work at that point as well.

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

regards, tom lane