Re: Do you know the reason for increased max latency due to xlog scaling?

On 2014-02-18 23:01:08 +0200, Heikki Linnakangas wrote:
> On 02/18/2014 10:51 PM, Andres Freund wrote:
> >On 2014-02-18 19:12:32 +0200, Heikki Linnakangas wrote:
> >>Yeah, I'm pretty sure that's because of the extra checkpoints. If you look
> >>at the individual test graphs, there are clear spikes in latency, but the
> >>latency is otherwise small. With a higher TPS, you reach checkpoint_segments
> >>quicker; I should've eliminated that effect in the tests I ran...
> >
> >I don't think that'd be a good idea. The number of full page writes so
> >greatly influences the WAL charactersistics, that changing checkpoint
> >segments would make the tests much harder to compare.
> 
> I was just thinking of bumping up checkpoint_segments so high that there are
> no checkpoints during any of the tests.

Hm. I actually think that full page writes are an interesting part of
this because they are so significantly differently sized than normal
records.

Greetings,

Andres Freund

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