Re: Just-in-time Background Writer Patch+Test Results

On Sat, 8 Sep 2007, Tom Lane wrote:

> I've already gotten flak about the current default of 200ms:
> https://bugzilla.redhat.com/show_bug.cgi?id=252129
> I can't imagine that folk with those types of goals will tolerate an
> un-tunable 10ms cycle.

That's the counter-example for why lowering the default is unacceptable I
was looking for. Scratch bgwriter_delay off the list of things that might
be fixed to a specific value.

Will return to the drawing board to figure out a way to incorporate what
I've learned about running at 10ms into a tuning plan that still works
fine at 200ms or higher. The good news as far as I'm concerned is that I
haven't had to adjust the code so far, just tweak the existing knobs.

> In fact, given the numbers you show here, I'd say you should leave the
> default cycle time at 200ms. The 10ms value is eating way more CPU and
> producing absolutely no measured benefit relative to 200ms...

My server is a bit underpowered to run at 10ms and gain anything when
doing a stress test like this; I was content that it didn't degrade
performance significantly, that was the best I could hope for. I would
expect the class of systems that Simon and Heikki are working with could
show significant benefit from running the BGW that often.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD