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

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.