我正在从一个Postgres表中聚合数据,查询大约需要2秒钟的时间,我希望将其减少到不到1秒钟。
请查看下面的执行详细信息:
查询
select
a.search_keyword,
hll_cardinality( hll_union_agg(a.users) ):: int as user_count,
hll_cardinality( hll_union_agg(a.sessions) ):: int as session_count,
sum(a.total) as keyword_count
from
rollup_day a
where
a.created_date between '2018-09-01' and '2019-09-30'
and a.tenant_id = '62850a62-19ac-477d-9cd7-837f3d716885'
group by
a.search_keyword
order by
session_count desc
limit 100;
表元数据
- 总行数 - 506527
- 基于列的复合索引 : tenant_id和created_date
查询计划
Custom Scan (cost=0.00..0.00 rows=0 width=0) (actual time=1722.685..1722.694 rows=100 loops=1)
Task Count: 1
Tasks Shown: All
-> Task
Node: host=localhost port=5454 dbname=postgres
-> Limit (cost=64250.24..64250.49 rows=100 width=42) (actual time=1783.087..1783.106 rows=100 loops=1)
-> Sort (cost=64250.24..64558.81 rows=123430 width=42) (actual time=1783.085..1783.093 rows=100 loops=1)
Sort Key: ((hll_cardinality(hll_union_agg(sessions)))::integer) DESC
Sort Method: top-N heapsort Memory: 33kB
-> GroupAggregate (cost=52933.89..59532.83 rows=123430 width=42) (actual time=905.502..1724.363 rows=212633 loops=1)
Group Key: search_keyword
-> Sort (cost=52933.89..53636.53 rows=281055 width=54) (actual time=905.483..1351.212 rows=280981 loops=1)
Sort Key: search_keyword
Sort Method: external merge Disk: 18496kB
-> Seq Scan on rollup_day a (cost=0.00..17890.22 rows=281055 width=54) (actual time=29.720..112.161 rows=280981 loops=1)
Filter: ((created_date >= '2018-09-01'::date) AND (created_date <= '2019-09-30'::date) AND (tenant_id = '62850a62-19ac-477d-9cd7-837f3d716885'::uuid))
Rows Removed by Filter: 225546
Planning Time: 0.129 ms
Execution Time: 1786.222 ms
Planning Time: 0.103 ms
Execution Time: 1722.718 ms
我尝试过的方法
- 我尝试在tenant_id和created_date上建立索引,但由于数据量太大,因此它总是进行顺序扫描而不是索引扫描以进行筛选。我阅读了相关资料并发现,如果返回的数据>总行数的5-10%,则Postgres查询引擎会切换到顺序扫描。请单击此处了解更多信息。
- 我将work_mem增加到100MB,但只能稍微提高性能。
非常感谢您的任何帮助。
更新
将work_mem设置为100MB后的查询计划
Custom Scan (cost=0.00..0.00 rows=0 width=0) (actual time=1375.926..1375.935 rows=100 loops=1)
Task Count: 1
Tasks Shown: All
-> Task
Node: host=localhost port=5454 dbname=postgres
-> Limit (cost=48348.85..48349.10 rows=100 width=42) (actual time=1307.072..1307.093 rows=100 loops=1)
-> Sort (cost=48348.85..48633.55 rows=113880 width=42) (actual time=1307.071..1307.080 rows=100 loops=1)
Sort Key: (sum(total)) DESC
Sort Method: top-N heapsort Memory: 35kB
-> GroupAggregate (cost=38285.79..43996.44 rows=113880 width=42) (actual time=941.504..1261.177 rows=172945 loops=1)
Group Key: search_keyword
-> Sort (cost=38285.79..38858.52 rows=229092 width=54) (actual time=941.484..963.061 rows=227261 loops=1)
Sort Key: search_keyword
Sort Method: quicksort Memory: 32982kB
-> Seq Scan on rollup_day_104290 a (cost=0.00..17890.22 rows=229092 width=54) (actual time=38.803..104.350 rows=227261 loops=1)
Filter: ((created_date >= '2019-01-01'::date) AND (created_date <= '2019-12-30'::date) AND (tenant_id = '62850a62-19ac-477d-9cd7-837f3d716885'::uuid))
Rows Removed by Filter: 279266
Planning Time: 0.131 ms
Execution Time: 1308.814 ms
Planning Time: 0.112 ms
Execution Time: 1375.961 ms
更新2
在创建了一个按created_date索引并将work_mem增加到120MB后,
create index date_idx on rollup_day(created_date);
总行数为:12,124,608
查询计划如下:
Custom Scan (cost=0.00..0.00 rows=0 width=0) (actual time=2635.530..2635.540 rows=100 loops=1)
Task Count: 1
Tasks Shown: All
-> Task
Node: host=localhost port=9702 dbname=postgres
-> Limit (cost=73545.19..73545.44 rows=100 width=51) (actual time=2755.849..2755.873 rows=100 loops=1)
-> Sort (cost=73545.19..73911.25 rows=146424 width=51) (actual time=2755.847..2755.858 rows=100 loops=1)
Sort Key: (sum(total)) DESC
Sort Method: top-N heapsort Memory: 35kB
-> GroupAggregate (cost=59173.97..67948.97 rows=146424 width=51) (actual time=2014.260..2670.732 rows=296537 loops=1)
Group Key: search_keyword
-> Sort (cost=59173.97..60196.85 rows=409152 width=55) (actual time=2013.885..2064.775 rows=410618 loops=1)
Sort Key: search_keyword
Sort Method: quicksort Memory: 61381kB
-> Index Scan using date_idx_102913 on rollup_day_102913 a (cost=0.42..21036.35 rows=409152 width=55) (actual time=0.026..183.370 rows=410618 loops=1)
Index Cond: ((created_date >= '2018-01-01'::date) AND (created_date <= '2018-12-31'::date))
Filter: (tenant_id = '12850a62-19ac-477d-9cd7-837f3d716885'::uuid)
Planning Time: 0.135 ms
Execution Time: 2760.667 ms
Planning Time: 0.090 ms
Execution Time: 2635.568 ms
hll_union_agg
需要这么多内存。 - user330315