On 12/01/07, Tobias Brox <tobias@xxxxxxxxxxxxx> wrote:
We have a table with a timestamp attribute (event_time) and a state flag which usually changes value around the event_time (it goes to 4). Now we have more than two years of events in the database, and around 5k of future events. It is important to frequently pick out "overdue events", say: select * from events where state<>4 and event_time<now() This query would usually yield between 0 and 100 rows - however, the planner doesn't see the correlation betewen state and event_time - since most of the events have event_time<now, the planner also assumes most of the events with state<>4 has event_time<now, so the expected number of rows is closer to 5k. This matters, because I have a query with joins, and I would really benefit from nested loops. (I've tried replacing "now()" above with different timestamps from the future and the past. I'm using pg 8.2) Any suggestions?
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. Peter.
