由于PostgreSQL没有提供类似Oracle的自治事务控制功能,本节介绍了如何使用dblink实现简单的自治事务控制. **样例** 安装dblink插件,验证dblink可连接至本地PG ``` [local]:5432 pg12@testdb=# create extension dblink; ERROR: extension "dblink" already exists Time: 1.128 ms [local]:5432 pg12@testdb=# select t1.* from dblink('host=/tmp port=5432 dbname=testdb user=pg12','select * from t1') as t1(id int,c1 int,c2 int) limit 1; id | c1 | c2 ----+----+---- 4 | 4 | 4 (1 row) Time: 1413.943 ms (00:01.414) ``` 创建数据表和存储过程 ``` [local]:5432 pg12@testdb=# drop table if exists log; DROP TABLE Time: 38.531 ms [local]:5432 pg12@testdb=# CREATE TABLE log( pg12@testdb(# msg text not null, pg12@testdb(# sender_ts timestamptz not null, pg12@testdb(# local_ts timestamptz default now() pg12@testdb(# ); CREATE TABLE Time: 8.686 ms [local]:5432 pg12@testdb=# CREATE OR REPLACE FUNCTION log_dblink(msg text) pg12@testdb-# RETURNS void pg12@testdb-# LANGUAGE sql pg12@testdb-# AS $function$ pg12@testdb$# select dblink('host=/tmp port=5432 user=pg12 dbname=testdb', pg12@testdb$# format('insert into log select %L, %L', msg, clock_timestamp()::text)) pg12@testdb$# $function$; CREATE FUNCTION Time: 3.657 ms ``` 测试验证,启动事务,调用函数,然后rollback ``` [local]:5432 pg12@testdb=# begin; BEGIN Time: 1.293 ms [local]:5432 pg12@testdb=#* select log_dblink('log message'); log_dblink ------------ (1 row) Time: 16.394 ms [local]:5432 pg12@testdb=#* rollback; ROLLBACK Time: 0.845 ms ``` 通过dblink执行的SQL主事务隔离,已commit ``` [local]:5432 pg12@testdb=# select * from log; msg | sender_ts | local_ts -------------+-------------------------------+------------------------------- log message | 2019-08-05 14:23:30.459183+08 | 2019-08-05 14:23:30.468047+08 (1 row) Time: 0.695 ms ``` **参考资料** [PostgreSQL DBA(58) - DBLink](http://blog.itpub.net/6906/viewspace-2650936/) [Implementing Autonomous Transactions in Postgres](https://www.cybertec-postgresql.com/en/implementing-autonomous-transactions-in-postgres/)