> From: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@postgresql.org]On Behalf Of Steven
Rosenstein
> >> I don't think EXPLAIN ANALYZE puts that much overhead on a query.
I think you're being overly optimistic. The explain shows that the
Materialize subnode is being entered upwards of 32 million times:
-> Materialize (cost=505.06..511.38 rows=632 width=4) (actual time=0.00..0.02 rows=43 loops=752066)
43 * 752066 = 32338838. The instrumentation overhead is basically two
gettimeofday() kernel calls per node entry. Doing the math shows that
your machine is able to do gettimeofday() in about half a microsecond,
which isn't stellar but it's not all that slow for a kernel call.
(What's the platform here, anyway?) Nonetheless it's a couple of times
larger than the actual time needed to pull a row from a materialized
array ...
The real answer to your question is "IN (subselect) sucks before PG 7.4;
get a newer release".
regards, tom lane
