Re: Speed up Clog Access by increasing CLOG buffers

On Tue, Sep 27, 2016 at 5:15 PM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> So, I got the results from 3.10.101 (only the pgbench data), and it looks
> like this:
>
> 3.10.101 1 8 16 32 64 128 192
> --------------------------------------------------------------------
> granular-locking 2582 18492 33416 49583 53759 53572 51295
> no-content-lock 2580 18666 33860 49976 54382 54012 51549
> group-update 2635 18877 33806 49525 54787 54117 51718
> master 2630 18783 33630 49451 54104 53199 50497
>
> So 3.10.101 performs even better tnan 3.2.80 (and much better than 4.5.5),
> and there's no sign any of the patches making a difference.

I'm sure that you mentioned this upthread somewhere, but I can't
immediately find it. What scale factor are you testing here?

It strikes me that the larger the scale factor, the more
CLogControlLock contention we expect to have. We'll pretty much do
one CLOG access per update, and the more rows there are, the more
chance there is that the next update hits an "old" row that hasn't
been updated in a long time. So a larger scale factor also increases
the number of active CLOG pages and, presumably therefore, the amount
of CLOG paging activity.

--
Robert Haas
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