Really poor gist index performance with tstzrange types
Am I doing something silly? Or is the row-estimation for gist indexes not
even close in this case?
-- This is not running inside a transaction.
drop table if exists f;
create table f (duration tstzrange);
insert into f
select tstzrange(now() - '1 month'::interval, now() - '1
sec'::interval) from generate_series(1, 100000);
create index on f using gist(duration);
analyze f;
select count(*) from f where tstzrange(now(), now(), '[]') << duration;
-- returns 0
explain analyze
select count(*) from f where tstzrange(now(), now(), '[]') << duration;
Aggregate (cost=2720.36..2720.37 rows=1 width=0) (actual
time=55.374..55.374 rows=1 loops=1)
-> Seq Scan on f (cost=0.00..2637.02 rows=33334 width=0) (actual
time=55.369..55.369 rows=0 loops=1)
Filter: (tstzrange(now(), now(), '[]'::text) << duration)
Rows Removed by Filter: 100000
Total runtime: 55.407 ms
Joe Van Dyk <joe@tanga.com> writes:
Am I doing something silly? Or is the row-estimation for gist indexes not
even close in this case?
9.2 didn't have any logic for estimating range << conditions. I see
reasonable estimates for this case in HEAD, though, presumably thanks
to work by Alexander Korotkov.
regards, tom lane
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On Tue, Jun 11, 2013 at 5:13 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Joe Van Dyk <joe@tanga.com> writes:
Am I doing something silly? Or is the row-estimation for gist indexes not
even close in this case?9.2 didn't have any logic for estimating range << conditions. I see
reasonable estimates for this case in HEAD, though, presumably thanks
to work by Alexander Korotkov.
I just wanted to add that rewriting the << condition the way shown
below might partially solve the problem.
where
tstzrange(now(), now(), '[]') < duration and
not tstzrange(now(), now(), '[]') && duration
And here is the result.
[local]:5432 grayhemp@grayhemp=#
explain analyze
select count(*) from f where tstzrange(now(), now(), '[]') << duration;
QUERY PLAN
------------------------------------------------------------------------------------------------------------
Aggregate (cost=2720.17..2720.18 rows=1 width=0) (actual
time=109.161..109.163 rows=1 loops=1)
-> Seq Scan on f (cost=0.00..2636.84 rows=33331 width=0) (actual
time=109.148..109.148 rows=0 loops=1)
Filter: (tstzrange(now(), now(), '[]'::text) << duration)
Rows Removed by Filter: 100000
Total runtime: 109.210 ms
(5 rows)
Time: 109.837 ms
[local]:5432 grayhemp@grayhemp=#
explain analyze
select count(*) from f where tstzrange(now(), now(), '[]') < duration
and not tstzrange(now(), now(), '[]') && duration;
QUERY
PLAN
------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=2646.39..2646.40 rows=1 width=0) (actual
time=0.042..0.043 rows=1 loops=1)
-> Bitmap Heap Scan on f (cost=926.55..2563.48 rows=33164
width=0) (actual time=0.035..0.035 rows=0 loops=1)
Recheck Cond: (tstzrange(now(), now(), '[]'::text) < duration)
Filter: (NOT (tstzrange(now(), now(), '[]'::text) && duration))
-> Bitmap Index Scan on f_duration_idx1 (cost=0.00..918.26
rows=33331 width=0) (actual time=0.030..0.030 rows=0 loops=1)
Index Cond: (tstzrange(now(), now(), '[]'::text) < duration)
Total runtime: 0.098 ms
(7 rows)
Time: 0.801 ms
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Kind regards,
Sergey Konoplev
PostgreSQL Consultant and DBA
Profile: http://www.linkedin.com/in/grayhemp
Phone: USA +1 (415) 867-9984, Russia +7 (901) 903-0499, +7 (988) 888-1979
Skype: gray-hemp
Jabber: gray.ru@gmail.com
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