极乐门资源网

postgresql insert into select无法使用并行查询的解决
数据库 2024/12/22 佚名
2 0
极乐门资源网 Design By www.ioogu.com

本文信息基于PG13.1。

从PG9.6开始支持并行查询。PG11开始支持CREATE TABLE … AS、SELECT INTO以及CREATE MATERIALIZED VIEW的并行查询。

先说结论：

换用create table as 或者select into或者导入导出。

首先跟踪如下查询语句的执行计划：

select count(*) from test t1,test1 t2 where t1.id = t2.id ;

postgres=# explain analyze select count(*) from test t1,test1 t2 where t1.id = t2.id ;
                                    QUERY PLAN                                    
--------------------------------------------------------------------------------------------------------------------------------------------------------
 Finalize Aggregate (cost=34244.16..34244.17 rows=1 width=8) (actual time=683.246..715.324 rows=1 loops=1)
  -> Gather (cost=34243.95..34244.16 rows=2 width=8) (actual time=681.474..715.311 rows=3 loops=1)
     Workers Planned: 2
     Workers Launched: 2
     -> Partial Aggregate (cost=33243.95..33243.96 rows=1 width=8) (actual time=674.689..675.285 rows=1 loops=3)
        -> Parallel Hash Join (cost=15428.00..32202.28 rows=416667 width=0) (actual time=447.799..645.689 rows=333333 loops=3)
           Hash Cond: (t1.id = t2.id)
           -> Parallel Seq Scan on test t1 (cost=0.00..8591.67 rows=416667 width=4) (actual time=0.025..74.010 rows=333333 loops=3)
           -> Parallel Hash (cost=8591.67..8591.67 rows=416667 width=4) (actual time=260.052..260.053 rows=333333 loops=3)
              Buckets: 131072 Batches: 16 Memory Usage: 3520kB
              -> Parallel Seq Scan on test1 t2 (cost=0.00..8591.67 rows=416667 width=4) (actual time=0.032..104.804 rows=333333 loops=3)
 Planning Time: 0.420 ms
 Execution Time: 715.447 ms
(13 rows)

可以看到走了两个Workers。

下边看一下insert into select：

postgres=# explain analyze insert into va select count(*) from test t1,test1 t2 where t1.id = t2.id ;     
                                  QUERY PLAN                                  
--------------------------------------------------------------------------------------------------------------------------------------------------
 Insert on va (cost=73228.00..73228.02 rows=1 width=4) (actual time=3744.179..3744.187 rows=0 loops=1)
  -> Subquery Scan on "*SELECT*" (cost=73228.00..73228.02 rows=1 width=4) (actual time=3743.343..3743.352 rows=1 loops=1)
     -> Aggregate (cost=73228.00..73228.01 rows=1 width=8) (actual time=3743.247..3743.254 rows=1 loops=1)
        -> Hash Join (cost=30832.00..70728.00 rows=1000000 width=0) (actual time=1092.295..3511.301 rows=1000000 loops=1)
           Hash Cond: (t1.id = t2.id)
           -> Seq Scan on test t1 (cost=0.00..14425.00 rows=1000000 width=4) (actual time=0.030..421.537 rows=1000000 loops=1)
           -> Hash (cost=14425.00..14425.00 rows=1000000 width=4) (actual time=1090.078..1090.081 rows=1000000 loops=1)
              Buckets: 131072 Batches: 16 Memory Usage: 3227kB
              -> Seq Scan on test1 t2 (cost=0.00..14425.00 rows=1000000 width=4) (actual time=0.021..422.768 rows=1000000 loops=1)
 Planning Time: 0.511 ms
 Execution Time: 3745.633 ms
(11 rows)

可以看到并没有Workers的指示，没有启用并行查询。

即使开启强制并行，也无法走并行查询。

postgres=# set force_parallel_mode =on;
SET
postgres=# explain analyze insert into va select count(*) from test t1,test1 t2 where t1.id = t2.id ;
                                  QUERY PLAN                                  
--------------------------------------------------------------------------------------------------------------------------------------------------
 Insert on va (cost=73228.00..73228.02 rows=1 width=4) (actual time=3825.042..3825.049 rows=0 loops=1)
  -> Subquery Scan on "*SELECT*" (cost=73228.00..73228.02 rows=1 width=4) (actual time=3824.976..3824.984 rows=1 loops=1)
     -> Aggregate (cost=73228.00..73228.01 rows=1 width=8) (actual time=3824.972..3824.978 rows=1 loops=1)
        -> Hash Join (cost=30832.00..70728.00 rows=1000000 width=0) (actual time=1073.587..3599.402 rows=1000000 loops=1)
           Hash Cond: (t1.id = t2.id)
           -> Seq Scan on test t1 (cost=0.00..14425.00 rows=1000000 width=4) (actual time=0.034..414.965 rows=1000000 loops=1)
           -> Hash (cost=14425.00..14425.00 rows=1000000 width=4) (actual time=1072.441..1072.443 rows=1000000 loops=1)
              Buckets: 131072 Batches: 16 Memory Usage: 3227kB
              -> Seq Scan on test1 t2 (cost=0.00..14425.00 rows=1000000 width=4) (actual time=0.022..400.624 rows=1000000 loops=1)
 Planning Time: 0.577 ms
 Execution Time: 3825.923 ms
(11 rows)

原因在官方文档有写：

The query writes any data or locks any database rows. If a query contains a data-modifying operation either at the top level or within a CTE, no parallel plans for that query will be generated. As an exception, the commands CREATE TABLE … AS, SELECT INTO, and CREATE MATERIALIZED VIEW which create a new table and populate it can use a parallel plan.

解决方案有如下三种：

1.select into

postgres=# explain analyze select count(*) into vaa from test t1,test1 t2 where t1.id = t2.id ;
                                    QUERY PLAN                                    
--------------------------------------------------------------------------------------------------------------------------------------------------------
 Finalize Aggregate (cost=34244.16..34244.17 rows=1 width=8) (actual time=742.736..774.923 rows=1 loops=1)
  -> Gather (cost=34243.95..34244.16 rows=2 width=8) (actual time=740.223..774.907 rows=3 loops=1)
     Workers Planned: 2
     Workers Launched: 2
     -> Partial Aggregate (cost=33243.95..33243.96 rows=1 width=8) (actual time=731.408..731.413 rows=1 loops=3)
        -> Parallel Hash Join (cost=15428.00..32202.28 rows=416667 width=0) (actual time=489.880..700.830 rows=333333 loops=3)
           Hash Cond: (t1.id = t2.id)
           -> Parallel Seq Scan on test t1 (cost=0.00..8591.67 rows=416667 width=4) (actual time=0.033..87.479 rows=333333 loops=3)
           -> Parallel Hash (cost=8591.67..8591.67 rows=416667 width=4) (actual time=266.839..266.840 rows=333333 loops=3)
              Buckets: 131072 Batches: 16 Memory Usage: 3520kB
              -> Parallel Seq Scan on test1 t2 (cost=0.00..8591.67 rows=416667 width=4) (actual time=0.058..106.874 rows=333333 loops=3)
 Planning Time: 0.319 ms
 Execution Time: 783.300 ms
(13 rows)

2.create table as

postgres=# explain analyze create table vb as select count(*) from test t1,test1 t2 where t1.id = t2.id ;
                                   QUERY PLAN                                    
-------------------------------------------------------------------------------------------------------------------------------------------------------
 Finalize Aggregate (cost=34244.16..34244.17 rows=1 width=8) (actual time=540.120..563.733 rows=1 loops=1)
  -> Gather (cost=34243.95..34244.16 rows=2 width=8) (actual time=537.982..563.720 rows=3 loops=1)
     Workers Planned: 2
     Workers Launched: 2
     -> Partial Aggregate (cost=33243.95..33243.96 rows=1 width=8) (actual time=526.602..527.136 rows=1 loops=3)
        -> Parallel Hash Join (cost=15428.00..32202.28 rows=416667 width=0) (actual time=334.532..502.793 rows=333333 loops=3)
           Hash Cond: (t1.id = t2.id)
           -> Parallel Seq Scan on test t1 (cost=0.00..8591.67 rows=416667 width=4) (actual time=0.018..57.819 rows=333333 loops=3)
           -> Parallel Hash (cost=8591.67..8591.67 rows=416667 width=4) (actual time=189.502..189.503 rows=333333 loops=3)
              Buckets: 131072 Batches: 16 Memory Usage: 3520kB
              -> Parallel Seq Scan on test1 t2 (cost=0.00..8591.67 rows=416667 width=4) (actual time=0.023..77.786 rows=333333 loops=3)
 Planning Time: 0.189 ms
 Execution Time: 565.448 ms
(13 rows)

3.或者通过导入导出的方式，例如：

psql -h localhost -d postgres -U postgres -c "select count(*) from test t1,test1 t2 where t1.id = t2.id " -o result.csv -A -t -F ","
psql -h localhost -d postgres -U postgres -c "COPY va FROM 'result.csv' WITH (FORMAT CSV, DELIMITER ',', HEADER FALSE, ENCODING 'windows-1252')"

一些场景下也会比非并行快。

标签：
postgresql,并行查询,postgresql,insert,into,select
极乐门资源网 Design By www.ioogu.com
极乐门资源网 免责声明：本站文章均来自网站采集或用户投稿，网站不提供任何软件下载或自行开发的软件！ 如有用户或公司发现本站内容信息存在侵权行为，请邮件告知！ 858582#qq.com
极乐门资源网 Design By www.ioogu.com

评论“postgresql insert into select无法使用并行查询的解决”

暂无postgresql insert into select无法使用并行查询的解决的评论...
www.ioogu.com 极乐门资源网
139,976影音资源
144,792福利资源
21,817软件资源
631,128技术资源

《魔兽世界》大逃杀！60人新游玩模式《强袭风暴》3月21日上线

暴雪近日发布了《魔兽世界》10.2.6 更新内容，新游玩模式《强袭风暴》即将于3月21 日在亚服上线，届时玩家将前往阿拉希高地展开一场 60 人大逃杀对战。

艾泽拉斯的冒险者已经征服了艾泽拉斯的大地及遥远的彼岸。他们在对抗世界上最致命的敌人时展现出过人的手腕，并且成功阻止终结宇宙等级的威胁。当他们在为即将于《魔兽世界》资料片《地心之战》中来袭的萨拉塔斯势力做战斗准备时，他们还需要在熟悉的阿拉希高地面对一个全新的敌人──那就是彼此。在《巨龙崛起》10.2.6 更新的《强袭风暴》中，玩家将会进入一个全新的海盗主题大逃杀式限时活动，其中包含极高的风险和史诗级的奖励。

《强袭风暴》不是普通的战场，作为一个独立于主游戏之外的活动，玩家可以用大逃杀的风格来体验《魔兽世界》，不分职业、不分装备（除了你在赛局中捡到的），光是技巧和战略的强弱之分就能决定出谁才是能坚持到最后的赢家。本次活动将会开放单人和双人模式，玩家在加入海盗主题的预赛大厅区域前，可以从强袭风暴角色画面新增好友。游玩游戏将可以累计名望轨迹，《巨龙崛起》和《魔兽世界：巫妖王之怒 经典版》的玩家都可以获得奖励。

更新日志

友情链接

杰晶网络 DDR爱好者之家 桃源资源网 杰网资源 富贵资源网 南强小屋 铁雪资源网 幽灵资源网 万梅资源网 狼山资源网 白云岛资源网 昆仑资源网 相思资源网 明霞山资源网 内蒙古资源网 黑松山资源网 茶园资源网 饿虎岗资源网 大旗谷资源网 常春岛资源网 岱庙资源网 兴国资源网 快活林资源网 蝙蝠岛资源网 帝王谷资源网 白云城资源网 伏龙阁资源网 清风细雨楼 天枫庄资源网 圆月山庄资源网 无争山庄资源网 神水资源网 移花宫资源网 神剑山庄资源网 无为清净楼资源网 金钱帮资源网 丐帮资源网 华山资源网 极乐门资源网 小李飞刀资源网 凤求凰客栈 风云阁资源网 金狮镖局 鸳鸯亭资源网 千金楼资源网 更多链接
极乐门资源网 Design By www.ioogu.com