我正在运行Geodjango/Postgres 9.1/PostGIS,我试图让以下查询(和其他人喜欢它)运行得更快。更快地创建Postgres查询。更多索引?
[查询剪断,为简洁]
SELECT "crowdbreaks_incomingkeyword"."keyword_id"
, COUNT("crowdbreaks_incomingkeyword"."keyword_id") AS "cnt"
FROM "crowdbreaks_incomingkeyword"
INNER JOIN "crowdbreaks_tweet"
ON ("crowdbreaks_incomingkeyword"."tweet_id"
= "crowdbreaks_tweet"."tweet_id")
LEFT OUTER JOIN "crowdbreaks_place"
ON ("crowdbreaks_tweet"."place_id"
= "crowdbreaks_place"."place_id")
WHERE (("crowdbreaks_tweet"."coordinates"
@ ST_GeomFromEWKB(E'\\001 ... \\000\\000\\000\\[email protected]'::bytea)
OR ST_Overlaps("crowdbreaks_place"."bounding_box"
, ST_GeomFromEWKB(E'\\001...00\\000\\[email protected]'::bytea)
))
AND "crowdbreaks_tweet"."created_at" > E'2012-04-17 15:46:12.109893'
AND "crowdbreaks_tweet"."created_at" < E'2012-04-18 15:46:12.109899')
GROUP BY "crowdbreaks_incomingkeyword"."keyword_id"
, "crowdbreaks_incomingkeyword"."keyword_id"
;
这里是crowdbreaks_tweet表的样子:
\d+ crowdbreaks_tweet;
Table "public.crowdbreaks_tweet"
Column | Type | Modifiers | Storage | Description
---------------+--------------------------+-----------+----------+-------------
tweet_id | bigint | not null | plain |
tweeter | bigint | not null | plain |
text | text | not null | extended |
created_at | timestamp with time zone | not null | plain |
country_code | character varying(3) | | extended |
place_id | character varying(32) | | extended |
coordinates | geometry | | main |
Indexes:
"crowdbreaks_tweet_pkey" PRIMARY KEY, btree (tweet_id)
"crowdbreaks_tweet_coordinates_id" gist (coordinates)
"crowdbreaks_tweet_created_at" btree (created_at)
"crowdbreaks_tweet_place_id" btree (place_id)
"crowdbreaks_tweet_place_id_like" btree (place_id varchar_pattern_ops)
Check constraints:
"enforce_dims_coordinates" CHECK (st_ndims(coordinates) = 2)
"enforce_geotype_coordinates" CHECK (geometrytype(coordinates) = 'POINT'::text OR coordinates IS NULL)
"enforce_srid_coordinates" CHECK (st_srid(coordinates) = 4326)
Foreign-key constraints:
"crowdbreaks_tweet_place_id_fkey" FOREIGN KEY (place_id) REFERENCES crowdbreaks_place(place_id) DEFERRABLE INITIALLY DEFERRED
Referenced by:
TABLE "crowdbreaks_incomingkeyword" CONSTRAINT "crowdbreaks_incomingkeyword_tweet_id_fkey" FOREIGN KEY (tweet_id) REFERENCES crowdbreaks_tweet(tweet_id) DEFERRABLE INITIALLY DEFERRED
TABLE "crowdbreaks_tweetanswer" CONSTRAINT "crowdbreaks_tweetanswer_tweet_id_id_fkey" FOREIGN KEY (tweet_id_id) REFERENCES crowdbreaks_tweet(tweet_id) DEFERRABLE INITIALLY DEFERRED
Has OIDs: no
这里是解释分析查询:
HashAggregate (cost=184022.03..184023.18 rows=115 width=4) (actual time=6381.707..6381.769 rows=62 loops=1)
-> Hash Join (cost=103857.48..183600.24 rows=84357 width=4) (actual time=1745.449..6377.505 rows=3453 loops=1)
Hash Cond: (crowdbreaks_incomingkeyword.tweet_id = crowdbreaks_tweet.tweet_id)
-> Seq Scan on crowdbreaks_incomingkeyword (cost=0.00..36873.97 rows=2252597 width=12) (actual time=0.008..2136.839 rows=2252597 loops=1)
-> Hash (cost=102535.68..102535.68 rows=80544 width=8) (actual time=1744.815..1744.815 rows=3091 loops=1)
Buckets: 4096 Batches: 4 Memory Usage: 32kB
-> Hash Left Join (cost=16574.93..102535.68 rows=80544 width=8) (actual time=112.551..1740.651 rows=3091 loops=1)
Hash Cond: ((crowdbreaks_tweet.place_id)::text = (crowdbreaks_place.place_id)::text)
Filter: ((crowdbreaks_tweet.coordinates @ '0103000020E61000000100000005000000AE47E17A141E5FC00000000000003840AE47E17A141E5FC029ED0DBE30B14840A4703D0AD7A350C029ED0DBE30B14840A4703D0AD7A350C00000000000003840AE47E17A141E5FC00000000000003840'::geometry) OR ((crowdbreaks_place.bounding_box && '0103000020E61000000100000005000000AE47E17A141E5FC00000000000003840AE47E17A141E5FC029ED0DBE30B14840A4703D0AD7A350C029ED0DBE30B14840A4703D0AD7A350C00000000000003840AE47E17A141E5FC00000000000003840'::geometry) AND _st_overlaps(crowdbreaks_place.bounding_box, '0103000020E61000000100000005000000AE47E17A141E5FC00000000000003840AE47E17A141E5FC029ED0DBE30B14840A4703D0AD7A350C029ED0DBE30B14840A4703D0AD7A350C00000000000003840AE47E17A141E5FC00000000000003840'::geometry)))
-> Bitmap Heap Scan on crowdbreaks_tweet (cost=15874.18..67060.28 rows=747873 width=125) (actual time=96.012..940.462 rows=736784 loops=1)
Recheck Cond: ((created_at > '2012-04-17 15:46:12.109893+00'::timestamp with time zone) AND (created_at < '2012-04-18 15:46:12.109899+00'::timestamp with time zone))
-> Bitmap Index Scan on crowdbreaks_tweet_crreated_at (cost=0.00..15687.22 rows=747873 width=0) (actual time=94.259..94.259 rows=736784 loops=1)
Index Cond: ((created_at > '2012-04-17 15:46:12.109893+00'::timestamp with time zone) AND (created_at < '2012-04-18 15:46:12.109899+00'::timestamp with time zone))
-> Hash (cost=217.11..217.11 rows=6611 width=469) (actual time=15.926..15.926 rows=6611 loops=1)
Buckets: 1024 Batches: 4 Memory Usage: 259kB
-> Seq Scan on crowdbreaks_place (cost=0.00..217.11 rows=6611 width=469) (actual time=0.005..6.908 rows=6611 loops=1)
Total runtime: 6381.903 ms
(17 rows)
这对于查询来说是相当糟糕的运行时间。理想情况下,我希望在一两秒内得到结果。
我已经增加了Postgres的shared_buffers到2GB(我有8GB的RAM),但除此之外,我不知道该怎么办。我有什么选择?我应该减少联接吗?我还有其他的指标吗? crowdbreaks_incomingkeyword的顺序扫描对我来说没有意义。它是其他表的外键表,因此它有索引。
如果我'设置启用seqscan关闭';'在运行解释分析之前,查询时间缩短为1.8秒。然而,我读的所有内容都说我不应该这样做。 – Khandelwal 2012-04-19 16:23:22
我在这里粘贴了您的EXPLAIN输出:http://explain.depesz.com/s/EfH以获得更好的视图。 – 2012-04-19 16:43:18
BTW:在GROUP BY子句中复制术语'crowdbreaks_incomingkeyword“。”keyword_id'会产生什么样的影响? (可能是优化器忘记删除冗余,并将组的特殊性计算为1 /平方(组数) – wildplasser 2012-04-19 22:10:54