作者
digoal
日期
2021-04-03
标签
PostgreSQL , sharding , fdw , postgres_fdw , keep_connections
背景
postgres_fdw server option : keep_connections , 保持foreign server连接.
- keep_connections off表示foreign 事务结束后 立即释放foreign连接.
- keep_connections on表示保持foreign连接. 直到退出当前会话. 好处是高并发的foreign oltp业务, 减少大量建连接到开销. 坏处是总连接数可能增多, 访问过foreign server的连接都会被保持, 可以通过管理函数主动释放.
《怎么看待PostgreSQL sharding插件: citus - 对比PG 社区基于 postgres_fdw 的sharding》
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=b1be3074ac719ce8073fba35d4c8b52fb4ddd0c3
```
postgres_fdw: Add option to control whether to keep connections open.
author Fujii Masao fujii@postgresql.org
Fri, 2 Apr 2021 10:45:42 +0000 (19:45 +0900)
committer Fujii Masao fujii@postgresql.org
Fri, 2 Apr 2021 10:45:42 +0000 (19:45 +0900)
commit b1be3074ac719ce8073fba35d4c8b52fb4ddd0c3
tree 4a7b836541eb0d7df10a6b83e951c7f9f673cc3e tree
parent 9c5f67fd6256246b2a788a8feb1d42b79dcd0448 commit | diff
postgres_fdw: Add option to control whether to keep connections open.
This commit adds a new option keep_connections that controls
whether postgres_fdw keeps the connections to the foreign server open
so that the subsequent queries can re-use them. This option can only be
specified for a foreign server. The default is on. If set to off,
all connections to the foreign server will be discarded
at the end of transaction. Closed connections will be re-established
when they are necessary by future queries using a foreign table.
This option is useful, for example, when users want to prevent
the connections from eating up the foreign servers connections
capacity.
Author: Bharath Rupireddy
Reviewed-by: Alexey Kondratov, Vignesh C, Fujii Masao
Discussion: https://postgr.es/m/CALj2ACVvrp5=AVp2PupEm+nAC8S4buqR3fJMmaCoc7ftT0aD2A@mail.gmail.com
```
+-- Test foreign server level option keep_connections
+-- ===================================================================
+-- By default, the connections associated with foreign server are cached i.e.
+-- keep_connections option is on. Set it to off.
+ALTER SERVER loopback OPTIONS (keep_connections 'off');
+-- connection to loopback server is closed at the end of xact
+-- as keep_connections was set to off.
+SELECT 1 FROM ft1 LIMIT 1;
+ ?column?
+----------
+ 1
+(1 row)
+
+-- No cached connections, so no records should be output.
+SELECT server_name FROM postgres_fdw_get_connections() ORDER BY 1;
+ server_name
+-------------
+(0 rows)
+
+ALTER SERVER loopback OPTIONS (SET keep_connections 'on');
+-- ===================================================================
PostgreSQL 许愿链接
您的愿望将传达给PG kernel hacker、数据库厂商等, 帮助提高数据库产品质量和功能, 说不定下一个PG版本就有您提出的功能点. 针对非常好的提议，奖励限量版PG文化衫、纪念品、贴纸、PG热门书籍等，奖品丰富，快来许愿。开不开森.
9.9元购买3个月阿里云RDS PostgreSQL实例
PostgreSQL 解决方案集合
德哥 / digoal's github - 公益是一辈子的事.
