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Thread: Postgresql 11.3 doesn't use gist index on polygon column

Postgresql 11.3 doesn't use gist index on polygon column

From
Вадим Самохин
Date:
Hi there,
1. I have a table that looks like this:
create table zonez (p polygon);
2. I have an index that looks like this:
create index zonez__p2 on zonez using gist(p poly_ops);
3. I inserted several records in that table, it looks like:
postgres=# select * from zonez ;
                     p                    
-------------------------------------------
 ((1,1),(1,5),(5,5),(5,1))
 ((1,2),(1,5),(5,5),(5,1))
 ((1,3),(1,5),(5,5),(5,1))
 ((1,4),(1,5),(5,5),(5,1))
 ((1,6),(1,5),(5,5),(5,1))
 ((1,7),(1,5),(5,5),(5,1))
 ((1,7),(1,5),(5,5),(500000,1000))
 ((1,7),(1,5),(5,5),(52.654987,37.123789))
(8 rows)
4. I've "turned off" seqscan: set enable_seqscan = off;
5. I've issued vacuum analyze
6. But postgresql still doesn't want to use my index:
postgres=# explain analyze select * from zonez where '(2,2)'::point <@ p;
                                                     QUERY PLAN                                                      
---------------------------------------------------------------------------------------------------------------------
 Seq Scan on zonez  (cost=10000000000.00..10000000001.10 rows=1 width=101) (actual time=0.013..0.018 rows=2 loops=1)
   Filter: ('(2,2)'::point <@ p)
   Rows Removed by Filter: 6
 Planning Time: 0.069 ms
 Execution Time: 0.036 ms
(5 rows)

How come? Is it an index that should look different, or is it really more expensive than 10000000001.10?

Re: Postgresql 11.3 doesn't use gist index on polygon column

From
Tom Lane
Date:
=?UTF-8?B?0JLQsNC00LjQvCDQodCw0LzQvtGF0LjQvQ==?= <samokhinvadim@gmail.com> writes:
> 6. But postgresql still doesn't want to use my index:
> postgres=# explain analyze select * from zonez where '(2,2)'::point <@ p;

It can't, because "polygon @> point" isn't one of the operators supported
by that opclass.  You could use a polygon comparison:

=# \dAo gist poly_ops
               List of operators of operator families
  AM  | Operator family |       Operator       | Strategy | Purpose
------+-----------------+----------------------+----------+----------
 gist | poly_ops        | <<(polygon,polygon)  |        1 | search
 gist | poly_ops        | &<(polygon,polygon)  |        2 | search
 gist | poly_ops        | &&(polygon,polygon)  |        3 | search
 gist | poly_ops        | &>(polygon,polygon)  |        4 | search
 gist | poly_ops        | >>(polygon,polygon)  |        5 | search
 gist | poly_ops        | ~=(polygon,polygon)  |        6 | search
 gist | poly_ops        | @>(polygon,polygon)  |        7 | search
 gist | poly_ops        | <@(polygon,polygon)  |        8 | search
 gist | poly_ops        | &<|(polygon,polygon) |        9 | search
 gist | poly_ops        | <<|(polygon,polygon) |       10 | search
 gist | poly_ops        | |>>(polygon,polygon) |       11 | search
 gist | poly_ops        | |&>(polygon,polygon) |       12 | search
 gist | poly_ops        | <->(polygon,point)   |       15 | ordering
(13 rows)

            regards, tom lane

Re: Postgresql 11.3 doesn't use gist index on polygon column

From
Вадим Самохин
Date:
Oh, got it, thanks!

чт, 17 нояб. 2022 г. в 18:52, Tom Lane <tgl@sss.pgh.pa.us>:
Вадим Самохин <samokhinvadim@gmail.com> writes:
> 6. But postgresql still doesn't want to use my index:
> postgres=# explain analyze select * from zonez where '(2,2)'::point <@ p;

It can't, because "polygon @> point" isn't one of the operators supported
by that opclass.  You could use a polygon comparison:

=# \dAo gist poly_ops
               List of operators of operator families
  AM  | Operator family |       Operator       | Strategy | Purpose 
------+-----------------+----------------------+----------+----------
 gist | poly_ops        | <<(polygon,polygon)  |        1 | search
 gist | poly_ops        | &<(polygon,polygon)  |        2 | search
 gist | poly_ops        | &&(polygon,polygon)  |        3 | search
 gist | poly_ops        | &>(polygon,polygon)  |        4 | search
 gist | poly_ops        | >>(polygon,polygon)  |        5 | search
 gist | poly_ops        | ~=(polygon,polygon)  |        6 | search
 gist | poly_ops        | @>(polygon,polygon)  |        7 | search
 gist | poly_ops        | <@(polygon,polygon)  |        8 | search
 gist | poly_ops        | &<|(polygon,polygon) |        9 | search
 gist | poly_ops        | <<|(polygon,polygon) |       10 | search
 gist | poly_ops        | |>>(polygon,polygon) |       11 | search
 gist | poly_ops        | |&>(polygon,polygon) |       12 | search
 gist | poly_ops        | <->(polygon,point)   |       15 | ordering
(13 rows)

                        regards, tom lane