Re: [ADMIN] ORDER BY too slow in Foreign Table using postgres_fdw - Mailing list pgsql-admin
From | Luan Huynh |
---|---|
Subject | Re: [ADMIN] ORDER BY too slow in Foreign Table using postgres_fdw |
Date | |
Msg-id | CAAP3KKFKeq3NUPuYhDSyqaaLcsKMLDn=Qx5_XQSuzWNXa5JD2g@mail.gmail.com Whole thread Raw |
In response to | Re: [ADMIN] ORDER BY too slow in Foreign Table using postgres_fdw (Samed YILDIRIM <samed@reddoc.net>) |
List | pgsql-admin |
Thank your help, Samed.
That idea is great.
After apply your idea, for testing, I try to add some columns in the remote table, then try to filter them. As a result, the query will slow again (due to order by).
On Tue, Jul 18, 2017 at 7:38 PM, Samed YILDIRIM <samed@reddoc.net> wrote:
Hi Luan,Sort operation is performed on local postgres server, not on remote. Because of that, local postgresql server gets all rows matched by filter and then sort them. If your code always sort the results, you can just create a view on remote postgres with order by clause and then create a foreign table pointing to the view. By using a view like that, sorting is performed on remote server.On remote Postgrescreate view user_info_vw as select id,info from user_info order by id;On local Postgrescreate foreign table user_info (id bigint, info jsonb) server luan_server options (schema_name 'public', table_name 'user_info_vw');Before viewpostgres=# explain analyze SELECT id, infoFROM user_infoWHERE info ->> 'key1'= '1' order by id limit 10;QUERY PLAN ------------------------------------------------------------ ------------------------------ ------------------------------ --------- Limit (cost=153.28..153.29 rows=6 width=40) (actual time=7512.755..7512.759 rows=10 loops=1)-> Sort (cost=153.28..153.29 rows=6 width=40) (actual time=7512.754..7512.757 rows=10 loops=1)Sort Key: idSort Method: top-N heapsort Memory: 26kB-> Foreign Scan on user_info (cost=100.00..153.20 rows=6 width=40) (actual time=0.962..7351.989 rows=1187840 loops=1)Filter: ((info ->> 'key1'::text) = '1'::text)Rows Removed by Filter: 786432Planning time: 0.089 msExecution time: 7513.322 ms(9 rows)After viewexplain analyze SELECT id, infoFROM user_infoWHERE info ->> 'key1'= '1' LIMIT 10;QUERY PLAN ------------------------------------------------------------ ------------------------------ ------------------------- Limit (cost=100.00..153.20 rows=6 width=40) (actual time=0.678..0.684 rows=10 loops=1)-> Foreign Scan on user_info (cost=100.00..153.20 rows=6 width=40) (actual time=0.677..0.681 rows=10 loops=1)Filter: ((info ->> 'key1'::text) = '1'::text)Rows Removed by Filter: 4Planning time: 0.060 msExecution time: 1.167 ms(6 rows)postgres=# SELECT id, infopostgres-# FROM user_infopostgres-# WHERE info ->> 'key1'= '1' LIMIT 10;id | info----+---------------------------- 1 | {"key1": 1, "key2": 0.678}2 | {"key1": 1, "key2": 0.678}3 | {"key1": 1, "key2": 1.0}4 | {"key1": 1, "key2": 0.986}7 | {"key1": 1, "key2": 0.678}8 | {"key1": 1, "key2": 1.0}9 | {"key1": 1, "key2": 0.986}12 | {"key1": 1, "key2": 0.678}13 | {"key1": 1, "key2": 1.0}14 | {"key1": 1, "key2": 0.986}(10 rows)Best regards.İyi çalışmalar.Samed YILDIRIM18.07.2017, 10:06, "Luan Huynh" <nnhluan@gmail.com>:Hi all,On PostgreSQL v.9.6, when using postgres_fdw, I got an issue with "ORDER BY" (here's my question on stackexchange ).Query on Foreign TableSELECT id, infoFROM user_infoWHERE info ->> 'key1'= '1'ORDER BY idLIMIT 10;Limit (cost=10750829.63..10750829.65 rows=10 width=40) (actual time=550059.320..550059.326 rows=10 loops=1) -> Sort (cost=10750829.63..10751772.77 rows=377257 width=40) (actual time=550059.318..550059.321 rows=10 loops=1) Sort Key: idSort Method: top-N heapsort Memory: 26kB-> Foreign Scan on user_info (cost=100.00..10742677.24 rows=377257 width=40) (actual time=1.413..536718.366 rows=68281020 loops=1)Filter: ((info ->> 'key1'::text) = '1'::text)Rows Removed by Filter: 7170443Planning time: 4.097 msExecution time: 550059.597 msQuery on remote serverEXPLAIN ANALYSESELECT id, infoFROM user_info_rawWHERE info ->> 'key1'= '1'ORDER BY idLIMIT 10;Limit (cost=0.57..1296.95 rows=10 width=59) (actual time=0.043..0.073 rows=10 loops=1)-> Index Scan using idx_user_info_raw_info on user_info_raw (cost=0.57..68882850.88 rows=531346 width=59) (actual time=0.042..0.070 rows=10 loops=1)Filter: ((info ->> 'key1'::text) = '1'::text)Planning time: 0.192 msExecution time: 0.102 msPlease help me to figure out the solution for that issue .Thank you
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