早上好我在JOIN每个表中都有一些表格，我不明白为什么我们会在聚合上浪费时间;查询是：
EXPLAIN ANALYZE SELECT COUNT(handsData.id) as hands
FROM
stats stats JOIN heronames players on (stats.heronameid = players.heronameid)
JOIN PREFLOP preflopStats on preflopStats.preflopstatsid = stats.preflopstatsid
JOIN FLOP flopStats on flopStats.flopstatsid = stats.flopstatsid
JOIN TURN turnStats on turnStats.turnstatsid = stats.turnstatsid
JOIN RIVER riverStats on riverStats.riverstatsid = stats.riverstatsid
JOIN hands AS handsData on handsData.id = stats.handid
JOIN (SELECT tournamentid FROM tournaments WHERE tournamentcode IS NULL) AS smallTournaments ON handsData.tournamentid = smallTournaments.tournamentid
JOIN (SELECT pokertypeid AS ptid, pokertype AS pokertypeName FROM poker_types) AS poker_types ON handsData.pokerType = poker_types.ptid
WHERE players.heroName='RubenGrimes' AND players.networkNumber=2
在stats，flopstats，turnstats和riverstas表格中我们有大约700k的记录。
手表上有大约120k的记录。在其他表上有一些k记录。
"Aggregate (cost=5219.65..5219.66 rows=1 width=8) (actual time=2080.230..2080.230 rows=1 loops=1)"
" -> Nested Loop (cost=10.47..5219.31 rows=138 width=8) (actual time=20.190..2065.578 rows=119755 loops=1)"
" Join Filter: (handsdata.pokertype = (public.poker_types.pokertypeid)::double precision)"
" Rows Removed by Join Filter: 239510"
" -> Nested Loop (cost=10.47..5211.03 rows=138 width=16) (actual time=20.169..1953.894 rows=119755 loops=1)"
" -> Nested Loop (cost=10.47..4235.67 rows=138 width=20) (actual time=20.145..1641.112 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..3260.20 rows=138 width=4) (actual time=20.134..1315.970 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..2732.02 rows=138 width=8) (actual time=20.100..1047.149 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..2203.84 rows=138 width=12) (actual time=20.065..774.187 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..1675.66 rows=138 width=16) (actual time=20.027..496.012 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..1147.48 rows=138 width=20) (actual time=19.983..183.725 rows=119937 loops=1)"
" -> Seq Scan on heronames players (cost=0.00..226.41 rows=1 width=4) (actual time=1.669..1.682 rows=1 loops=1)"
" Filter: ((heroname = 'RubenGrimes'::text) AND (networknumber = 2))"
" Rows Removed by Filter: 9826"
" -> Bitmap Heap Scan on stats (cost=10.47..918.63 rows=244 width=24) (actual time=18.308..143.084 rows=119937 loops=1)"
" Recheck Cond: (heronameid = players.heronameid)"
" -> Bitmap Index Scan on "stats index" (cost=0.00..10.41 rows=244 width=0) (actual time=15.829..15.829 rows=119937 loops=1)"
" Index Cond: (heronameid = players.heronameid)"
" -> Index Only Scan using "preflop index" on preflop preflopstats (cost=0.00..3.82 rows=1 width=8) (actual time=0.002..0.002 rows=1 loops=119937)"
" Index Cond: (preflopstatsid = stats.preflopstatsid)"
" Heap Fetches: 0"
" -> Index Only Scan using "flop index" on flop flopstats (cost=0.00..3.82 rows=1 width=8) (actual time=0.002..0.002 rows=1 loops=119937)"
" Index Cond: (flopstatsid = stats.flopstatsid)"
" Heap Fetches: 0"
" -> Index Only Scan using "turn index" on turn turnstats (cost=0.00..3.82 rows=1 width=8) (actual time=0.002..0.002 rows=1 loops=119937)"
" Index Cond: (turnstatsid = stats.turnstatsid)"
" Heap Fetches: 0"
" -> Index Only Scan using "river index" on river riverstats (cost=0.00..3.82 rows=1 width=8) (actual time=0.002..0.002 rows=1 loops=119937)"
" Index Cond: (riverstatsid = stats.riverstatsid)"
" Heap Fetches: 0"
" -> Index Scan using hands_pkey on hands handsdata (cost=0.00..7.06 rows=1 width=20) (actual time=0.002..0.002 rows=1 loops=119937)"
" Index Cond: (id = stats.handid)"
" -> Index Scan using "tournaments index" on tournaments (cost=0.00..7.06 rows=1 width=8) (actual time=0.002..0.002 rows=1 loops=119937)"
" Index Cond: (tournamentid = handsdata.tournamentid)"
" Filter: (tournamentcode IS NULL)"
" Rows Removed by Filter: 0"
" -> Materialize (cost=0.00..1.04 rows=3 width=4) (actual time=0.000..0.000 rows=3 loops=119755)"
" -> Seq Scan on poker_types (cost=0.00..1.03 rows=3 width=4) (actual time=0.010..0.010 rows=3 loops=1)"
任何改善我们加入的建议？
提前致谢
编辑：
我添加了两个缺失的索引，现在：
"Aggregate (cost=4537.05..4537.06 rows=1 width=8) (actual time=4726.083..4726.083 rows=1 loops=1)"
" -> Nested Loop (cost=10.47..4536.70 rows=138 width=8) (actual time=41.193..4692.321 rows=119755 loops=1)"
" Join Filter: (handsdata.pokertype = (public.poker_types.pokertypeid)::double precision)"
" Rows Removed by Join Filter: 239510"
" -> Nested Loop (cost=10.47..4528.42 rows=138 width=16) (actual time=41.144..4438.428 rows=119755 loops=1)"
" -> Nested Loop (cost=10.47..4017.53 rows=138 width=20) (actual time=41.100..3656.244 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..3042.06 rows=138 width=4) (actual time=41.081..2925.372 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..2513.88 rows=138 width=8) (actual time=41.064..2318.648 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..1985.70 rows=138 width=12) (actual time=41.046..1708.789 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..1457.52 rows=138 width=16) (actual time=41.028..1084.847 rows=119937 loops=1)"
" -> Nested Loop (cost=10.47..929.34 rows=138 width=20) (actual time=40.982..388.839 rows=119937 loops=1)"
" -> Index Scan using "big index" on heronames players (cost=0.00..8.27 rows=1 width=4) (actual time=0.078..0.079 rows=1 loops=1)"
" Index Cond: ((networknumber = 2) AND (heroname = 'RubenGrimes'::text))"
" -> Bitmap Heap Scan on stats (cost=10.47..918.63 rows=244 width=24) (actual time=40.889..301.217 rows=119937 loops=1)"
" Recheck Cond: (heronameid = players.heronameid)"
" -> Bitmap Index Scan on "stats index" (cost=0.00..10.41 rows=244 width=0) (actual time=35.179..35.179 rows=119937 loops=1)"
" Index Cond: (heronameid = players.heronameid)"
" -> Index Only Scan using "preflop index" on preflop preflopstats (cost=0.00..3.82 rows=1 width=8) (actual time=0.005..0.005 rows=1 loops=119937)"
" Index Cond: (preflopstatsid = stats.preflopstatsid)"
" Heap Fetches: 0"
" -> Index Only Scan using "flop index" on flop flopstats (cost=0.00..3.82 rows=1 width=8) (actual time=0.004..0.004 rows=1 loops=119937)"
" Index Cond: (flopstatsid = stats.flopstatsid)"
" Heap Fetches: 0"
" -> Index Only Scan using "turn index" on turn turnstats (cost=0.00..3.82 rows=1 width=8) (actual time=0.004..0.004 rows=1 loops=119937)"
" Index Cond: (turnstatsid = stats.turnstatsid)"
" Heap Fetches: 0"
" -> Index Only Scan using "river index" on river riverstats (cost=0.00..3.82 rows=1 width=8) (actual time=0.004..0.004 rows=1 loops=119937)"
" Index Cond: (riverstatsid = stats.riverstatsid)"
" Heap Fetches: 0"
" -> Index Scan using hands_pkey on hands handsdata (cost=0.00..7.06 rows=1 width=20) (actual time=0.005..0.005 rows=1 loops=119937)"
" Index Cond: (id = stats.handid)"
" -> Index Only Scan using "tournament big index" on tournaments (cost=0.00..3.69 rows=1 width=8) (actual time=0.005..0.006 rows=1 loops=119937)"
" Index Cond: ((tournamentcode IS NULL) AND (tournamentid = handsdata.tournamentid))"
" Heap Fetches: 0"
" -> Materialize (cost=0.00..1.04 rows=3 width=4) (actual time=0.000..0.001 rows=3 loops=119755)"
" -> Seq Scan on poker_types (cost=0.00..1.03 rows=3 width=4) (actual time=0.029..0.031 rows=3 loops=1)"
"Total runtime: 4726.684 ms"
我认为真正的问题是：
-> Bitmap Index Scan on "stats index" (cost=0.00..10.41 rows=244 width=0) (actual time=35.179..35.179 rows=119937 loops=1)"
" Index Cond: (heronameid = players.heronameid)"
答案 0 :(得分：0)
您计划中突出的事项包括：
跟进您的修改：Bitmap Index Scan on "stats index"部分很好。真正的问题是错误的统计数据，导致嵌套的循环计划有大约120k行而不是预期的138.在每个表上运行analyze以查看它是否有所不同。在具有更高基数的stats表上，运行set statistics（请参阅：alter table）以在此之前稍微增加采样。
除此之外：你仍然有这个非常非常丑陋的问题：
Join Filter: (handsdata.pokertype = (public.poker_types.pokertypeid)::double precision)
Rows Removed by Join Filter: 239510"
施法相当快......除非你必须做240k次。