Ich vermute, dass Sie den Standardwert random_page_cost = 4 verwenden , was viel zu hoch ist, was den Index-Scan zu kostspielig macht.
Ich versuche die 2 Tabellen mit diesem Skript zu rekonstruieren:
CREATE TABLE replays_game (
id integer NOT NULL,
PRIMARY KEY (id)
);
CREATE TABLE replays_playeringame (
player_id integer NOT NULL,
game_id integer NOT NULL,
PRIMARY KEY (player_id, game_id),
CONSTRAINT replays_playeringame_game_fkey
FOREIGN KEY (game_id) REFERENCES replays_game (id)
);
CREATE INDEX ix_replays_playeringame_game_id
ON replays_playeringame (game_id);
-- 150k games
INSERT INTO replays_game
SELECT generate_series(1, 150000);
-- ~150k players, ~2 games each
INSERT INTO replays_playeringame
select trunc(random() * 149999 + 1), generate_series(1, 150000);
INSERT INTO replays_playeringame
SELECT *
FROM
(
SELECT
trunc(random() * 149999 + 1) as player_id,
generate_series(1, 150000) as game_id
) AS t
WHERE
NOT EXISTS (
SELECT 1
FROM replays_playeringame
WHERE
t.player_id = replays_playeringame.player_id
AND t.game_id = replays_playeringame.game_id
)
;
-- the heavy player with 3000 games
INSERT INTO replays_playeringame
select 999999, generate_series(1, 3000);
Mit dem Standardwert von 4:
game=# set random_page_cost = 4;
SET
game=# explain analyse SELECT "replays_game".*
FROM "replays_game"
INNER JOIN "replays_playeringame" ON "replays_game"."id" = "replays_playeringame"."game_id"
WHERE "replays_playeringame"."player_id" = 999999;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------------
Hash Join (cost=1483.54..4802.54 rows=3000 width=4) (actual time=3.640..110.212 rows=3000 loops=1)
Hash Cond: (replays_game.id = replays_playeringame.game_id)
-> Seq Scan on replays_game (cost=0.00..2164.00 rows=150000 width=4) (actual time=0.012..34.261 rows=150000 loops=1)
-> Hash (cost=1446.04..1446.04 rows=3000 width=4) (actual time=3.598..3.598 rows=3000 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 106kB
-> Bitmap Heap Scan on replays_playeringame (cost=67.54..1446.04 rows=3000 width=4) (actual time=0.586..2.041 rows=3000 loops=1)
Recheck Cond: (player_id = 999999)
-> Bitmap Index Scan on replays_playeringame_pkey (cost=0.00..66.79 rows=3000 width=0) (actual time=0.560..0.560 rows=3000 loops=1)
Index Cond: (player_id = 999999)
Total runtime: 110.621 ms
Nach dem Absenken auf 2:
game=# set random_page_cost = 2;
SET
game=# explain analyse SELECT "replays_game".*
FROM "replays_game"
INNER JOIN "replays_playeringame" ON "replays_game"."id" = "replays_playeringame"."game_id"
WHERE "replays_playeringame"."player_id" = 999999;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=45.52..4444.86 rows=3000 width=4) (actual time=0.418..27.741 rows=3000 loops=1)
-> Bitmap Heap Scan on replays_playeringame (cost=45.52..1424.02 rows=3000 width=4) (actual time=0.406..1.502 rows=3000 loops=1)
Recheck Cond: (player_id = 999999)
-> Bitmap Index Scan on replays_playeringame_pkey (cost=0.00..44.77 rows=3000 width=0) (actual time=0.388..0.388 rows=3000 loops=1)
Index Cond: (player_id = 999999)
-> Index Scan using replays_game_pkey on replays_game (cost=0.00..0.99 rows=1 width=4) (actual time=0.006..0.006 rows=1 loops=3000)
Index Cond: (id = replays_playeringame.game_id)
Total runtime: 28.542 ms
(8 rows)
Wenn Sie SSD verwenden, würde ich es weiter auf 1.1 senken.
Was Ihre letzte Frage betrifft, denke ich wirklich, dass Sie bei postgresql bleiben sollten. Ich habe Erfahrung mit postgresql und mssql, und ich muss den Aufwand in letzteres verdreifachen, damit es halb so gut funktioniert wie ersteres.
