Re: Planner statistics, correlations

Tobias Brox wrote:
> [Peter Childs - Fri at 08:56:54AM +0000]
>> Can you say what state might be rather than what it is not. I'm guess
>> that state is an int but there is only a limited list of possible
>> states, if you can say what it might be rather than what it is the
>> index is more liklly to be used.
>
>   explain select * from events where state in (1,2,3) and event_time<now()
>
> also estimates almost 5k of rows.

Try a partial index:
CREATE INDEX my_new_index ON events (event_time)
WHERE state in (1,2,3);

Now, if that doesn't work you might want to split the query into two...

SELECT * FROM events
WHERE state IN (1,2,3) AND event_time < '2007-01-01'::date
UNION ALL
SELECT * FROM events
WHERE state IN (1,2,3) AND event_time >= '2007-01-01'::date AND
event_time < now();

CREATE INDEX my_new_index ON events (event_time)
WHERE state in (1,2,3) AND event_time < '2007-01-01'::date;

CREATE INDEX event_time_state_idx ON events (event_time, state);

You'll want to replace the index/update the query once a year/month etc.

--
   Richard Huxton
   Archonet Ltd