Re: Why should such a simple query over indexed columns be so slow?

Pretty sure. I just ran the same query twice in a row
with enable_seqscan=true and the "actual time" was on the order of 42
seconds both times. With enable_seqscan=false, it was on the order 3
seconds. Going back to enable_seqscan=true, it's back to 42 seconds. Unless
you're saying that enable_seqscan is determining whether or not the data is
being cached....

On Mon, Jan 30, 2012 at 1:13 PM, Fernando Hevia <fhevia(at)gmail(dot)com> wrote:
>
> On Mon, Jan 30, 2012 at 17:35, Alessandro Gagliardi <alessandro(at)path(dot)com>wrote:
>
>> Well that was a *lot* faster:
>>
>> "HashAggregate (cost=156301.82..156301.83 rows=2 width=26) (actual
>> time=2692.806..2692.807 rows=2 loops=1)"
>> " -> Bitmap Heap Scan on blocks (cost=14810.54..155828.95 rows=472871
>> width=26) (actual time=289.828..1593.893 rows=575186 loops=1)"
>> " Recheck Cond: (created > '2012-01-29 00:00:00+00'::timestamp
>> with time zone)"
>> " Filter: (shared IS FALSE)"
>> " -> Bitmap Index Scan on blocks_created_idx
>> (cost=0.00..14786.89 rows=550404 width=0) (actual time=277.407..277.407
>> rows=706663 loops=1)"
>> " Index Cond: (created > '2012-01-29 00:00:00+00'::timestamp
>> with time zone)"
>> "Total runtime: 2693.107 ms"
>>
>>
> U sure the new timing isn't owed to cached data? If I am reading it
> correctly, from the latest explain you posted the Index Scan shouldn't have
> made a difference as it is reporting pretty much all rows in the table have
> created > 'yesterday'.
> If the number of rows with created < 'yesterday' isn't significant (~ over
> 25% with default config) a full scan will be chosen and it will probably be
> the better choice too.
>
>
>