[英]Reduce execution time of my query in postgresql
以下是我的查詢。 執行需要 9387.430 毫秒,對於這樣的請求來說肯定是太長了。 我希望能夠減少此執行時間。 你能幫我解決這個問題嗎? 我還提供了我的分析 output。
EXPLAIN ANALYZE
SELECT a.artist, b.artist, COUNT(*)
FROM release_has_artist a, release_has_artist b
WHERE a.release = b.release AND a.artist <> b.artist
GROUP BY(a.artist,b.artist)
ORDER BY (a.artist,b.artist);;
EXPLAIN ANALYZE的Output:
Sort (cost=1696482.86..1707588.14 rows=4442112 width=48) (actual time=9253.474..9314.510 rows=461386 loops=1)
Sort Key: (ROW(a.artist, b.artist))
Sort Method: external sort Disk: 24832kB
-> Finalize GroupAggregate (cost=396240.32..932717.19 rows=4442112 width=48) (actual time=1928.058..2911.463 rows=461386 loops=1)
Group Key: a.artist, b.artist
-> Gather Merge (cost=396240.32..860532.87 rows=3701760 width=16) (actual time=1928.049..2494.638 rows=566468 loops=1)
Workers Planned: 2
Workers Launched: 2
-> Partial GroupAggregate (cost=395240.29..432257.89 rows=1850880 width=16) (actual time=1912.809..2156.951 rows=188823 loops=3)
Group Key: a.artist, b.artist
-> Sort (cost=395240.29..399867.49 rows=1850880 width=8) (actual time=1912.794..2003.776 rows=271327 loops=3)
Sort Key: a.artist, b.artist
Sort Method: external merge Disk: 4848kB
-> Merge Join (cost=0.85..177260.72 rows=1850880 width=8) (actual time=2.143..1623.628 rows=271327 loops=3)
Merge Cond: (a.release = b.release)
Join Filter: (a.artist <> b.artist)
Rows Removed by Join Filter: 687597
-> Parallel Index Only Scan using release_has_artist_pkey on release_has_artist a (cost=0.43..67329.73 rows=859497 width=8) (actual time=0.059..240.998 rows=687597 loops=3)
Heap Fetches: 711154
-> Index Only Scan using release_has_artist_pkey on release_has_artist b (cost=0.43..79362.68 rows=2062792 width=8) (actual time=0.072..798.402 rows=2329742 loops=3)
Heap Fetches: 2335683
Planning time: 2.101 ms
Execution time: 9387.430 ms
在您的EXPLAIN ANALYZE
output 中,有兩種Sort Method: external merge Disk: ####kB
,表示排序溢出到磁盤而不是work_mem
,因為 work_mem 大小不足。 嘗試將你的work_mem
增加到 32MB(30 可能沒問題,但我喜歡 8 的倍數),然后再試一次
Note that you can set work_mem
on a per-session basis, as a global change in work_mem
could potentially have negative side-effects, such as running out of memory, because postgresql.conf
-configured work_mem
is allocated for each session (basically, it有乘數效應)。
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