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Re: CLOG contention

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: CLOG contention
Date: 2012-01-05 19:57:01
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Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> I would like to do that, but I think we need to at least figure out a
> way to provide an escape hatch for people without much shared memory.
> We could do that, perhaps, by using a formula like this:

> 1 CLOG buffer per 128MB of shared_buffers, with a minimum of 8 and a
> maximum of 32

I would be in favor of that, or perhaps some other formula (eg, maybe
the minimum should be less than 8 for when you've got very little shmem).

I think that the reason it's historically been a constant is that the
original coding took advantage of having a compile-time-constant number
of buffers --- but since we went over to the common SLRU infrastructure
for several different logs, there's no longer any benefit whatever to
using a simple constant.

			regards, tom lane

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