Re: 2GB or not 2GB

Greg Smith wrote:
> On Wed, 28 May 2008, Josh Berkus wrote:
>
>> shared_buffers:  according to witnesses, Greg Smith presented at East
>> that
>> based on PostgreSQL's buffer algorithms, buffers above 2GB would not
>> really receive significant use.  However, Jignesh Shah has tested
>> that on
>> workloads with large numbers of connections, allocating up to 10GB
>> improves performance.
>
> Lies!  The only upper-limit for non-Windows platforms I mentioned was
> suggesting those recent tests at Sun showed a practical limit in the
> low multi-GB range.
>
> I've run with 4GB usefully for one of the multi-TB systems I manage,
> the main index on the most frequently used table is 420GB and anything
> I can do to keep the most popular parts of that pegged in memory seems
> to help. I haven't tried to isolate the exact improvement going from
> 2GB to 4GB with benchmarks though.
>
Yep its always the index that seems to benefit with high cache hits.. In
one of the recent tests what I end up doing is writing a select
count(*) from trade where t_id >= $1 and t_id < SOMEMAX just to kick in
index scan and get it in memory first. So higher the bufferpool better
the hit for index in it better the performance.

-Jignesh