Re: Weird issue with planner choosing seq scan

Sean Leach <sleach(at)wiggum(dot)com> writes:
> Now - here is prod:

> db=> select count(1) from u_counts;
> count
> ---------
> 3292215
> (1 row)

> -> Seq Scan on u_counts c (cost=0.00..444744.45
> rows=1106691 width=4) (actual time=1429.996..7893.178 rows=1036015
> loops=1)
> Filter: (stamp > (now() - '1 day'::interval))

Given that this scan actually is selecting about a third of the table,
I'm not sure that the planner is doing the wrong thing. It's hard to
see how an indexscan would be an improvement.

[ thinks for a bit... ] Actually, the problem might be the 3M
executions of now() and interval subtraction that you get in the seqscan
case. What results do you get if you write it with a sub-select like this:

explain analyze SELECT node,count(*) AS counts FROM u_counts
c,res r WHERE c.res_id=r.id AND stamp > (SELECT current_timestamp - interval
'1 day') AND r.rtype='udns' AND r.location=1 GROUP BY node;

regards, tom lane