Emanuel Calvo <postgres.arg@xxxxxxxxx> 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.) regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
