Re: Really poor gist index performance with tstzrange types

On Tue, Jun 11, 2013 at 5:13 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Joe Van Dyk <joe(at)tanga(dot)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(at)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(at)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

--
Kind regards,
Sergey Konoplev
PostgreSQL Consultant and DBA

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