Sean Chittenden <[EMAIL PROTECTED]> writes: > Getting the planner to pick > using the index to filter out data inserted in the last 3 days over > doing a seq scan... well, I don't know how you could do that without > changing the random_page_cost.
This sounds a *whole* lot like a correlation issue. If the data in question were scattered randomly in the table, it's likely that an indexscan would be a loser. The recently-inserted data is probably clustered near the end of the table (especially if they're doing VACUUM FULL after data purges; are they?). But the planner's correlation stats are much too crude to recognize that situation, if the rest of the table is not well-ordered. If their typical process involves a periodic data purge and then a VACUUM FULL, it might be worth experimenting with doing a CLUSTER on the timestamp index instead of the VACUUM FULL. The CLUSTER would reclaim space as effectively as VACUUM FULL + REINDEX, and it would leave the table with an unmistakable 1.0 correlation ... which should tilt the planner towards an indexscan without needing a physically impossible random_page_cost to do it. I think CLUSTER would probably be a little slower than VACUUM FULL but it's hard to be sure without trying. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to [EMAIL PROTECTED])