On Nov 27, 2006, at 2:23 , Brian Wipf wrote:
> On 26-Nov-06, at 11:25 PM, Jim C. Nasby wrote:
>> On Sat, Nov 18, 2006 at 08:13:26PM -0700, Brian Wipf wrote:
>>> It certainly is unfortunate if Guido's right and this is an upper
>>> limit for OS X. The performance benefit of having high
>>> shared_buffers
>>> on our mostly read database is remarkable.
>>
>> Got any data about that you can share? People have been wondering
>> about
>> cases where drastically increasing shared_buffers makes a difference.
>
> Unfortunately, there are more differences than just the
> shared_buffers setting in production right now; it's a completely
> different set up, so the numbers I have to compare against aren't
> particularly useful.
>
> When I get the chance, I will try to post data that shows the
> benefit of having a higher value of shared_buffers for our usage
> pattern (with all other settings being constant -- well, except
> maybe effective_cache_size). Basically, in our current
> configuration, we can cache all of the data we care about 99% of
> the time in about 3GB of shared_buffers. Having shared_buffers set
> to 512MB as it was originally, we were needlessly going to disk all
> of the time.
There is a known unfortunate limitation on Darwin for SysV shared
memory which, incidentally, does not afflict POSIX or mmap'd shared
memory.
http://archives.postgresql.org/pgsql-patches/2006-02/msg00176.php