Re: First query very slow. Solutions: memory, or settings, or SQL?

On Tue, Jul 21, 2009 at 6:12 PM, Peter Eisentraut<peter_e(at)gmx(dot)net> wrote:
> On Tuesday 21 July 2009 04:36:41 Phoenix Kiula wrote:
>> On Mon, Jul 20, 2009 at 2:04 PM, Peter Eisentraut<peter_e(at)gmx(dot)net> wrote:
>> > On Monday 20 July 2009 06:45:40 Phoenix Kiula wrote:
>> >> explain analyze select * from sites where user_id = 'phoenix' order by
>> >> id desc limit 10;
>> >>
>> >>                                                         QUERY PLAN
>> >> ------------------------------------------------------------------------
>> >>--- ----------------------------------------------------------- Limit
>> >> (cost=344.85..344.87 rows=10 width=262) (actual
>> >> time=5879.069..5879.167 rows=10 loops=1)
>> >>    ->  Sort  (cost=344.85..345.66 rows=323 width=262) (actual
>> >> time=5879.060..5879.093 rows=10 loops=1)
>> >>          Sort Key: id
>> >>          ->  Index Scan using new_idx_sites_userid on sites
>> >> (cost=0.00..331.39 rows=323 width=262) (actual time=44.408..5867.557
>> >> rows=2178 loops=1)
>> >>                Index Cond: ((user_id)::text = 'phoenix'::text)
>> >>  Total runtime: 5879.414 ms
>> >> (6 rows)
>> >
>> > The row estimate for the index scan is off.  Try reanalyzing, or increase
>> > the statistics target.
>>
>> How did you tell that the row estimate is off? I mean which numbers?
>
> Compare the rows=N figures for the estimate and the actual time.
>
>> Also, my statistics are already set pretty high. On "USER_ID" they are
>> at 100. Which columns should I increase the stats on, those in the
>> WHERE clause or those in the SELECT bit? The USER_ID and the
>> USER_KNOWN, which are in the WHERE clause, both have statistics of
>> 100! And USER_KNOWN is just a binary value (0 or 1) so I wonder what
>> purpose stats would serve?
>
> Well then that should be OK.
>

So what can I do to speed up? I now have about 8GB of memory (upgraded
yesterday). Would it help to increase the following:

shared_buffers = 512MB
effective_cache_size = 3GB

Both of these are conservative I think? My data size is about 30 GB
right now. Vacuum is all autovacuum as you see from settings I shared.

Any other ideas?