Message-ID: <4D508507.8010306@postnewspapers.com.au>
Date: Tue, 08 Feb 2011 07:49:27 +0800
From: Craig Ringer <craig@postnewspapers.com.au>
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To: Marti Raudsepp <marti@juffo.org>
CC: felix <crucialfelix@gmail.com>,
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Subject: Re: Really really slow select count(*)
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On 02/07/2011 06:30 PM, Marti Raudsepp wrote:
> On Mon, Feb 7, 2011 at 05:03, Craig Ringer<craig@postnewspapers.com.au>  wrote:
>> What would possibly help would be if Pg could fall back to lower
>> shared_buffers automatically, screaming about it in the logs but still
>> launching. OTOH, many people don't check the logs, so they'd think their
>> new setting had taken effect and it hadn't - you've traded one usability
>> problem for another. Even if Pg issued WARNING messages to each client
>> that connected, lots of (non-psql) clients don't display them, so many
>> users would never know.
>>
>> Do you have a suggestion about how to do this better? The current
>> approach is known to be rather unlovely, but nobody's come up with a
>> better one that works reasonably and doesn't trample on other System V
>> shared memory users that may exist on the system.
>
> We could do something similar to what Apache does -- provide distros
> with a binary to check the configuration file in advance. This check
> program is launched before the "restart" command, and if it fails, the
> server is not restarted.

That would work for config file errors (and would probably be a good 
idea) but won't help with bad shared memory configuration. When Pg is 
already running, it's usually not possible for a test program to claim 
the amount of shared memory the config file says to allocate, because Pg 
is already using it. Nonetheless, Pg will work fine when restarted.

--
Craig Ringer