Re: best way to query

Steve Clark <sclark(at)netwolves(dot)com> writes:
> Tom Lane wrote:
>> Also, whatever is the ORDER BY for?

> without the order by it wants to do a seq scan of t_unit_event_log.
> see below:
> explain select count(*) from t_event_ack_log where event_log_no not
> in (select event_log_no from t_unit_event_log);
> QUERY PLAN
> ----------------------------------------------------------------------------------------
> Aggregate (cost=12144872193.82..12144872193.82 rows=1 width=0)
> -> Seq Scan on t_event_ack_log (cost=0.00..12144871485.07
> rows=283497 width=0)
> Filter: (NOT (subplan))
> SubPlan
> -> Seq Scan on t_unit_event_log (cost=0.00..40286.56
> rows=1021156 width=4)
> (5 rows)

Hmm, the big problem with that isn't the seqscan but the lack of a
Materialize step to buffer it; which says to me that you're running a
pretty old Postgres version (8.0 or older). You should think about an
update if you're running into performance issues.

regards, tom lane