2011/11/10 Tom Lane <t...@sss.pgh.pa.us>: > Emanuel Calvo <postgres....@gmail.com> writes: >> postgres=# explain (buffers true, costs true, analyze true ) (select i >> from random_values) UNION ALL (SELECT NULL LIMIT 0); >> QUERY PLAN >> -------------------------------------------------------------------------------------------------------------------------------------- >> Result (cost=0.00..16897.02 rows=1000001 width=4) (actual >> time=0.203..13160.797 rows=1000000 loops=1) >> Buffers: shared hit=608 read=6289 >> -> Append (cost=0.00..16897.02 rows=1000001 width=4) (actual >> time=0.196..7925.918 rows=1000000 loops=1) >> Buffers: shared hit=608 read=6289 >> -> Seq Scan on random_values (cost=0.00..16897.00 >> rows=1000000 width=4) (actual time=0.190..2852.144 rows=1000000 >> loops=1) >> Buffers: shared hit=608 read=6289 >> -> Limit (cost=0.00..0.01 rows=1 width=0) (actual >> time=0.007..0.007 rows=0 loops=1) >> -> Result (cost=0.00..0.01 rows=1 width=0) (never executed) >> Total runtime: 15680.066 ms >> (9 rows) > >> 10 seconds to UNION *nothing*? Is an expected behavior? > > I'm inclined to read this result as showing that EXPLAIN ANALYZE has > very high per-node overhead on your machine. That is not too uncommon > on machines that don't have any way to read the clock without a kernel > call. You might try comparing straight execution times (without > using EXPLAIN) to get a clearer idea of how much it costs to pass data > through Append/Result. (It's not free, no.) >
Well, you are right. I'd executed without explain and the timing is not highly different. Thanks for the "EXPLAIN" ! -- -- Emanuel Calvo Helpame.com -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
