On Mon, 29 Sep 2003, Tom Lane wrote:
> Stephan Szabo <sszabo@megazone.bigpanda.com> writes:
> > As an update, so far I still am getting better results with NOT EXISTS
> > than the left join.
>
> Hm. Don't suppose you were using EXPLAIN ANALYZE so we could see what's
> happening? This is clearly a planner failure, although I'm unsure if we
> can expect the planner to get the right answer with no pg_statistic entries.
The left join one seems to give me values like the following:
At sort_mem=4096Merge Right Join (cost=9966071.76..10349763.45 rows=49501250 width=4)
(actual time=4383435.48..4383435.48 rows=0 loops=1) Merge Cond: (("outer".a = "inner".b) AND ("outer".b = "inner".c))
Filter:("outer".a IS NULL) -> Index Scan using pktest_a_key on pktest (cost=0.00..52.00
rows=1000 width=8) (actual time=17.82..1609.97 rows=10000 loops=1) -> Sort (cost=9966071.76..10089824.88
rows=49501250width=8) (actual
time=3876614.87..4157850.82 rows=50000000 loops=1) Sort Key: fktest.b, fktest.c -> Seq Scan on fktest
(cost=0.00..745099.00rows=49501250
width=8) (actual time=4.09..273798.65 rows=50000000 loops=1) Filter: ((b IS NOT NULL) AND (c IS NOT
NULL))Totalruntime: 4384366.79 msec
(9 rows)
At sort_mem=128000Merge Right Join (cost=69.32..134.00 rows=991 width=4) (actual
time=2183787.83..2183787.83 rows=0 loops=1) Merge Cond: (("outer".a = "inner".b) AND ("outer".b = "inner".c)) Filter:
("outer".aIS NULL) -> Index Scan using pktest_a_key on pktest (cost=0.00..52.00
rows=1000 width=8) (actual time=13.11..390.40 rows=10000
loops=1) -> Sort (cost=69.32..71.79 rows=991 width=8) (actual
time=1944240.67..2048954.65 rows=50000000 loops=1) Sort Key: fktest.b, fktest.c -> Seq Scan on fktest
(cost=0.00..20.00rows=991 width=8)
(actual time=2.61..225967.79 rows=50000000 loops=1) Filter: ((b IS NOT NULL) AND (c IS NOT NULL))Total
runtime:2184348.78 msec
I haven't finished a run with it doing an index scan on fktestyet,
still...
The not exists gives me:
Seq Scan on fktest (cost=0.00..242021289.48 rows=24750625 width=8)
(actual time=2032607.68..2032607.68 rows=0 loops=1) Filter: ((b IS NOT NULL) AND (c IS NOT NULL) AND (NOT (subplan)))
SubPlan -> Index Scan using pktest_a_key on pktest (cost=0.00..4.83 rows=1
width=0) (actual time=0.03..0.03 rows=1 loops=50000000) Index Cond: ((a = $0) AND (b = $1))Total runtime:
2032607.87msec
(6 rows)
But this time was one of the higher times for this query. I'd seen times
down at about 1400000 msec yesterday.
