Re: Auto-tuning work_mem and maintenance_work_mem

On Sat, Oct 12, 2013 at 3:07 AM, Magnus Hagander <magnus@hagander.net> wrote:
> On Oct 11, 2013 10:23 PM, "Josh Berkus" <josh@agliodbs.com> wrote:
>> On 10/11/2013 01:11 PM, Bruce Momjian wrote:
>> > In summary, I think we need to:
>> >
>> > *  decide on new defaults for work_mem and maintenance_work_mem
>> > *  add an initdb flag to allow users/packagers to set shared_bufffers?
>> > *  add an autovacuum_work_mem setting?
>> > *  change the default for temp_buffers?
>>
>> If we're changing defaults, bgwriter_lru_maxpages and vacuum_cost_limit
>> could also use a bump; those thresholds were set for servers with < 1GB
>> of RAM
>
> Uh, those are there to limit io and not memory, right? More memory isn't the
> reason to increase them, more io is. For people deploying on modern server
> hardware then yes it's often low, but for all those deploying in virtualized
> environments with io performance reminding you of the 1990ies, I'm not so
> sure it is...

bgwriter_lru_maxpages is clearly related to the size of
shared_buffers, although confusingly it is expressed as a number of
buffers, while shared_buffers is expressed as a quantity of memory.  I
think we might have done better to call the GUC
bgwriter_lru_maxpercent and make it a percentage of shared buffers.

-- 
Robert Haas
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