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Re: CLOG contention

From: Merlin Moncure <mmoncure(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: CLOG contention
Date: 2012-01-05 20:45:26
Message-ID: CAHyXU0wBiYz1nAHRho-4m4AYNdPm8_wsxud5GqnQ_rGe9uVkEQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Jan 5, 2012 at 2:25 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Jan 5, 2012 at 2:44 PM, Kevin Grittner
> <Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
>> If we go with such a formula, I think 32 MB would be a more
>> appropriate divisor than 128 MB.  Even on very large machines where
>> 32 CLOG buffers would be a clear win, we often can't go above 1 or 2
>> GB of shared_buffers without hitting latency spikes due to overrun
>> of the RAID controller cache.  (Now, that may change if we get DW
>> in, but that's not there yet.)  1 GB / 32 is 32 MB.  This would
>> leave CLOG pinned at the minimum of 8 buffers (64 KB) all the way up
>> to shared_buffers of 256 MB.
>
> That seems reasonable to me.

likewise (champion bikeshedder here).  It just so happens I typically
set 'large' server shared memory to 256mb.

merlin

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