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

On 2014-02-18 01:35:52 +0900, MauMau wrote:
> From: "Andres Freund" <andres@2ndquadrant.com>
> >On 2014-02-18 00:43:54 +0900, MauMau wrote:
> >>I'm worried about the big increase in max latency.  Do you know the
> >>cause?
> >>More frequent checkpoints caused by increased WAL volume thanks to
> >>enhanced
> >>performance?
> >
> >I don't see much evidence of increased latency there? You can't really
> >compare the latency when the throughput is significantly different.
> 
> For example, please see the max latencies of test set 2 (PG 9.3) and test
> set 4 (xlog scaling with padding).  They are 207.359 and 1219.422
> respectively.  The throughput is of course greatly improved, but I think the
> response time should not be sacrificed as much as possible.  There are some
> users who are sensitive to max latency, such as stock exchange and online
> games.

You need to compare both at the same throughput to have any meaningful
comparison.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services