我们的应用程序声明很慢，需要11秒以上，所以我想知道有没有办法优化它？
SQL语句
SELECT id FROM mapfriends.cell_forum_topic WHERE id in (
SELECT topicid FROM mapfriends.cell_forum_item WHERE skyid=103230293 GROUP BY topicid )
AND categoryid=29 AND hidden=false ORDER BY restoretime DESC LIMIT 10 OFFSET 0;
id
---------
2471959
2382296
1535967
2432006
2367281
2159706
1501759
1549304
2179763
1598043
(10 rows)
Time: 11444.976 ms
计划
friends=> explain SELECT id FROM friends.cell_forum_topic WHERE id in (
friends(> SELECT topicid FROM friends.cell_forum_item WHERE skyid=103230293 GROUP BY topicid)
friends-> AND categoryid=29 AND hidden=false ORDER BY restoretime DESC LIMIT 10 OFFSET 0;
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------
Limit (cost=1443.15..1443.15 rows=2 width=12)
-> Sort (cost=1443.15..1443.15 rows=2 width=12)
Sort Key: cell_forum_topic.restoretime
-> Nested Loop (cost=1434.28..1443.14 rows=2 width=12)
-> HashAggregate (cost=1434.28..1434.30 rows=2 width=4)
-> Index Scan using cell_forum_item_idx_skyid on cell_forum_item (cost=0.00..1430.49 rows=1516 width=4)
Index Cond: (skyid = 103230293)
-> Index Scan using cell_forum_topic_pkey on cell_forum_topic (cost=0.00..4.40 rows=1 width=12)
Index Cond: (cell_forum_topic.id = cell_forum_item.topicid)
Filter: ((NOT cell_forum_topic.hidden) AND (cell_forum_topic.categoryid = 29))
(10 rows)
Time: 1.109 ms
索引
friends=> \d cell_forum_item
Table "friends.cell_forum_item"
Column | Type | Modifiers
---------+--------------------------------+--------------------------------------------------------------
id | integer | not null default nextval('cell_forum_item_id_seq'::regclass)
topicid | integer | not null
skyid | integer | not null
content | character varying(200) |
addtime | timestamp(0) without time zone | default now()
ischeck | boolean |
Indexes:
"cell_forum_item_pkey" PRIMARY KEY, btree (id)
"cell_forum_item_idx" btree (topicid, skyid)
"cell_forum_item_idx_1" btree (topicid, id)
"cell_forum_item_idx_skyid" btree (skyid)
friends=> \d cell_forum_topic
Table "friends.cell_forum_topic"
Column | Type | Modifiers
-------------+--------------------------------+-------------------------------------------------------------------------------------
-
id | integer | not null default nextval(('"friends"."cell_forum_topic_id_seq"'::text)::regclass)
categoryid | integer | not null
topic | character varying | not null
content | character varying | not null
skyid | integer | not null
addtime | timestamp(0) without time zone | default now()
reference | integer | default 0
restore | integer | default 0
restoretime | timestamp(0) without time zone | default now()
locked | boolean | default false
settop | boolean | default false
hidden | boolean | default false
feature | boolean | default false
picid | integer | default 29249
managerid | integer |
imageid | integer | default 0
pass | boolean | default false
ischeck | boolean |
Indexes:
"cell_forum_topic_pkey" PRIMARY KEY, btree (id)
"idx_cell_forum_topic_1" btree (categoryid, settop, hidden, restoretime, skyid)
"idx_cell_forum_topic_2" btree (categoryid, hidden, restoretime, skyid)
"idx_cell_forum_topic_3" btree (categoryid, hidden, restoretime)
"idx_cell_forum_topic_4" btree (categoryid, hidden, restore)
"idx_cell_forum_topic_5" btree (categoryid, hidden, restoretime, feature)
"idx_cell_forum_topic_6" btree (categoryid, settop, hidden, restoretime)
解释分析
mapfriends=> explain analyze SELECT id FROM mapfriends.cell_forum_topic
mapfriends-> join (SELECT topicid FROM mapfriends.cell_forum_item WHERE skyid=103230293 GROUP BY topicid) as tmp
mapfriends-> on mapfriends.cell_forum_topic.id=tmp.topicid
mapfriends-> where categoryid=29 AND hidden=false ORDER BY restoretime DESC LIMIT 10 OFFSET 0;
QUERY PLAN
------------------------------------------------------------------------------------------------------------------------------------
----------------------------------------------
Limit (cost=1446.89..1446.90 rows=2 width=12) (actual time=18016.006..18016.013 rows=10 loops=1)
-> Sort (cost=1446.89..1446.90 rows=2 width=12) (actual time=18016.001..18016.002 rows=10 loops=1)
Sort Key: cell_forum_topic.restoretime
Sort Method: quicksort Memory: 25kB
-> Nested Loop (cost=1438.02..1446.88 rows=2 width=12) (actual time=16988.492..18015.869 rows=20 loops=1)
-> HashAggregate (cost=1438.02..1438.04 rows=2 width=4) (actual time=15446.735..15447.243 rows=610 loops=1)
-> Index Scan using cell_forum_item_idx_skyid on cell_forum_item (cost=0.00..1434.22 rows=1520 width=4) (actual time=302.378..15429.782 rows=7133 loops=1)
Index Cond: (skyid = 103230293)
-> Index Scan using cell_forum_topic_pkey on cell_forum_topic (cost=0.00..4.40 rows=1 width=12) (actual time=4.210..4.210 rows=0 loops=610)
Index Cond: (cell_forum_topic.id = cell_forum_item.topicid)
Filter: ((NOT cell_forum_topic.hidden) AND (cell_forum_topic.categoryid = 29))
Total runtime: 18019.461 ms
答案 0 :(得分：1)
您能否提供一些有关表格（统计数据）和配置的更多信息？
SELECT version();
SELECT category, name, setting FROM pg_settings WHERE name IN('effective_cache_size', 'enable_seqscan', 'shared_buffers');
SELECT * FROM pg_stat_user_tables WHERE relname IN('cell_forum_topic', 'cell_forum_item');
SELECT * FROM pg_stat_user_indexes WHERE relname IN('cell_forum_topic', 'cell_forum_item');
SELECT * FROM pg_stats WHERE tablename IN('cell_forum_topic', 'cell_forum_item');
在获取此数据之前，请使用ANALYZE。
看起来您的索引存在问题，这是所有查询花费所有时间的地方：
- ＆GT;使用cell_forum_item_idx_skyid进行索引扫描 cell_forum_item（费用= 0.00..1434.22 rows = 1520 width = 4）（实际 时间= 302.378..15429.782行= 7133 循环= 1）
如果您定期使用VACUUM FULL（不推荐！），索引膨胀可能是您的问题。 REINDEX可能是一个好主意，只是为了确定：
REINDEX TABLE cell_forum_item;
谈论索引，你可以放弃其中几个，这些已经过时了：
"idx_cell_forum_topic_6" btree (categoryid, settop, hidden, restoretime)
"idx_cell_forum_topic_3" btree (categoryid, hidden, restoretime)
其他索引具有相同的数据，也可以由数据库使用。
看起来你有几个问题：
但是，在你遇到新问题或其他问题之前，首先要让autovacuum回到正轨。
答案 1 :(得分：0)
问题不是由于缺乏查询计划的缓存，而是由于缺乏适当的索引而导致选择计划