Re: Weird issue with planner choosing seq scan - Mailing list pgsql-performance

Sean Leach <sleach@wiggum.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