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.
+1 on those.
Also, I have often had to bump cpu_tuple_cost into the 0.03 to 0.05
range to get a good plan. In general, this makes the exact
settings of *_page_cost less fussy, and I have hit situations where
I was completely unable to get a good plan to emerge without
bumping cpu_tuple_cost relative to the other cpu costs. I know that
it's possible to engineer a workload that shows any particular cost
adjustment to make things worse, but in real-life production
environments I have never seen an increase in this range make plan
choice worse.
Regarding the settings which have been the center of attention for
most of this thread, I have had very good luck with starting
work_mem at machine RAM * 0.25 / max_connections. I get the
impression that Josh regards that as too low. My guess is that he
deals more with data warehouse reporting systems than I do, where
larger settings are both more beneficial and less likely to cause
memory exhaustion than the typical systems I've worked with. That
is the big problem with auto-configuration -- it depends so much on
the workload. In the long run, an admission control policy and/or
adaptive configuration based on the observed workload seems like
what we *really* need.
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
