Re: Load Distributed Checkpoints, take 3

On Fri, 22 Jun 2007, Tom Lane wrote:

> Greg had worried about being able to turn this behavior off, so we'd
> still need at least a bool, and we might as well expose the fraction
> instead. I agree with removing the non-LRU part of the bgwriter's write
> logic though

If you accept that being able to turn LDC off is important, people who
aren't turning it on may still want the existing bgwriter_all_* settings
so they can keep running things the way they are now. It's certainly
reasonable to skip that code path when doing things the LDC way.

> True, you'd have to replay 1.5 checkpoint intervals on average instead
> of 0.5 (more or less, assuming checkpoints had been short). I don't
> think we're in the business of optimizing crash recovery time though.

If you're not, I think you should be. Keeping that replay interval time
down was one of the reasons why the people I was working with were
displeased with the implications of the very spread out style of some LDC
tunings. They were already unhappy with the implied recovery time of how
high they had to set checkpoint_settings for good performance, and making
it that much bigger aggrevates the issue. Given a knob where the LDC can
be spread out a bit but not across the entire interval, that makes it
easier to control how much expansion there is relative to the current
behavior.

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