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Re: CLOG contention

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: CLOG contention
Date: 2012-01-05 19:26:44
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Lists: pgsql-hackers
On Thu, Jan 5, 2012 at 2:21 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> On Thu, Jan 5, 2012 at 7:12 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Thu, Jan 5, 2012 at 11:10 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>>> Let's commit the change to 32.
>> 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
> We're talking about an extra 192KB or thereabouts and Clog buffers
> will only be the size of subtrans when we've finished.
> If you want to have a special low-memory option, then it would need to
> include many more things than clog buffers.
> Let's just use a constant value for clog buffers until the low-memory
> patch arrives.

Tom already stated that he found that unacceptable.  Unless he changes
his opinion, we're not going to get far if you're only happy if it's
constant and he's only happy if there's a formula.

On the other hand, I think there's a decent argument that he should
change his opinion, because 192kB of memory is not a lot.  However,
what I mostly want is something that nobody hates, so we can get it
committed and move on.

Robert Haas
The Enterprise PostgreSQL Company

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