On 03/04/2018 09:19 PM, Pavel Stehule wrote: > Hi > > Just curious > > postgres=# explain analyze select array_upper(array_agg(i),1) from > generate_series(1,100000) g(i); > QUERY > PLAN > --------------------------------------------------------------------------------------------------------------------------------- > Aggregate (cost=12.50..12.52 rows=1 width=4) (actual > time=43.164..43.164 rows=1 loops=1) > -> Function Scan on generate_series g (cost=0.00..10.00 rows=1000 > width=4) (actual time=19.150..31.083 rows=100000 loops=1) > Planning time: 0.100 ms > Execution time: 44.392 ms > (4 rows) > > postgres=# explain analyze select array_upper(array(select i from > generate_series(1,1000000) g(i)),1); > QUERY > PLAN > -------------------------------------------------------------------------------------------------------------------------------------- > Result (cost=10.00..10.01 rows=1 width=4) (actual > time=334.567..334.568 rows=1 loops=1) > InitPlan 1 (returns $0) > -> Function Scan on generate_series g (cost=0.00..10.00 rows=1000 > width=4) (actual time=141.503..254.483 rows=1000000 loops=1) > Planning time: 0.171 ms > Execution time: 339.057 ms > (5 rows) > > This code is about 8times slower >
Because you're passing 100000 in the first query and 1000000 in the second one. So it should be about 10x slower, more or less. regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
