Re: CLOG contention

Merlin Moncure <mmoncure@gmail.com>

From: Merlin Moncure <mmoncure@gmail.com>

To: Robert Haas <robertmhaas@gmail.com>

Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>, Simon Riggs <simon@2ndquadrant.com>, pgsql-hackers@postgresql.org, Tom Lane <tgl@sss.pgh.pa.us>

Date: 2012-01-05T20:45:26Z

Lists: pgsql-hackers

On Thu, Jan 5, 2012 at 2:25 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Jan 5, 2012 at 2:44 PM, Kevin Grittner
> <Kevin.Grittner@wicourts.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