PostgreSQL DBA(160) - pgAdmin(prepare transaction)

来源：这里教程网时间：2026-03-14 19:47:03 作者：

本节简单介绍了PostgreSQL中的Prepare Transaction，该特性会启用两阶段提交协议，可用于分布式事务。
比如以下一个应用场景:
数据分别存储在Oracle和PostgreSQL中,要求事务跨Oracle和PostgreSQL实现事务一致性,使用PG的Prepare Transaction可以(非完美)实现,不过需要引入更高层的事务管理器TM.
1.TM:开启PostgreSQL和Oracle事务
2.PostgreSQL:对数据进行处理
3.TM:对PG执行Prepare Transaction
4.Oracle:对数据进行处理
5.TM:PG提交事务
6.TM:如第5步出错,则回滚Oracle事务,否则提交Oracle事务
**启用两阶段提交特性**
```
[pg12@localhost pg121db]$ vim postgresql.conf 
[pg12@localhost pg121db]$ pg_ctl restart
waiting for server to shut down.... done
server stopped
waiting for server to start....2020-02-10 15:24:24.979 CST @ 2122  LOG:  starting PostgreSQL 12.1 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16), 64-bit
2020-02-10 15:24:24.980 CST @ 2122  LOG:  listening on IPv4 address "0.0.0.0", port 5120
2020-02-10 15:24:24.980 CST @ 2122  LOG:  listening on IPv6 address "::", port 5120
2020-02-10 15:24:24.985 CST @ 2122  LOG:  listening on Unix socket "/data/run/pg12/.s.PGSQL.5120"
2020-02-10 15:24:25.058 CST @ 2122  LOG:  redirecting log output to logging collector process
2020-02-10 15:24:25.058 CST @ 2122  HINT:  Future log output will appear in directory "pg_log".
 done
server started
[pg12@localhost pg121db]$ grep 'prepared' postgresql.conf 
max_prepared_transactions = 10		# zero disables the feature
# Caution: it is not advisable to set max_prepared_transactions nonzero unless
# you actively intend to use prepared transactions.
[pg12@localhost pg121db]$ 
```
**测试代码**
使用Java语言编写测试代码
```Java
/*
 *
 */
package testPG;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.sql.Statement;
public class TestBoolean {
	public static void main(String[] args) {
		System.out.println("---------- PG -----------");
		try (Connection conn4pg = DriverManager.getConnection("jdbc:postgresql://192.168.26.28:5120/testdb", "pg12",
				"pg12");
				Connection conn4ora = DriverManager.getConnection("jdbc:oracle:thin:@192.168.1.18:1521:orcl", "test",
						"test")) {
			// PG
			System.out.println("---------- PG -----------");
			conn4pg.setAutoCommit(false);
			boolean isOK = TestPG(conn4pg);
			if (!isOK) {
				System.out.println("---------- Fail! -----------");
				return;
			}
			TestPGPreTrans(conn4pg);
			// Oracle
			System.out.println("---------- Oracle -----------");
			conn4ora.setAutoCommit(false);
			isOK = TestOracle(conn4ora);
			// COMMIT
			conn4pg.setAutoCommit(true);
			TestPGEndPreTrans(conn4pg, isOK);
			conn4ora.commit();
			System.out.println("---------- DONE -----------");
		} catch (SQLException se) {
			System.out.println(se.getMessage());
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
		} // end try
	}
	public static boolean TestPG(Connection conn) {
		try (PreparedStatement pstmt = conn.prepareStatement("insert into t_pg(id,value) values(?,?)");) {
			pstmt.setInt(1, 1);
			pstmt.setString(2, "PostgreSQL");
			pstmt.execute();
			return true;
		} catch (SQLException se) {
			System.out.println(se.getMessage());
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
		} // end try
		return false;
	} // end
	public static void TestPGPreTrans(Connection conn) {
		try (Statement stmt = conn.createStatement()) {
			// 执行
			stmt.execute("prepare transaction 'pt1'");
			stmt.execute("commit");
		} catch (SQLException se) {
			System.out.println(se.getMessage());
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
		} // end try
	} // end
	public static void TestPGEndPreTrans(Connection conn, Boolean isOK) {
		try (Statement stmt = conn.createStatement()) {
			// 执行
			if (isOK) {
				stmt.execute("commit prepared 'pt1'");
			} else {
				stmt.execute("rollback prepared 'pt1'");
			}
		} catch (SQLException se) {
			System.out.println(se.getMessage());
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
		} // end try
	} // end
	public static boolean TestOracle(Connection conn) {
		try (PreparedStatement pstmt = conn.prepareStatement("insert into t_oracle(id,value) values(?,?)");) {
			pstmt.setInt(1, 1);
			pstmt.setString(2, "Oracle");
			pstmt.execute();
			return true;
		} catch (SQLException se) {
			System.out.println(se.getMessage());
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
		} // end try
		return false;
	} // end
} // end Class
```
*成功执行*
```
TEST-orcl@DESKTOP-V430TU3>select * from t_oracle;
        ID VALUE
---------- --------------------
         1 Oracle
[local:/data/run/pg12]:5120 pg12@testdb=# select * from t_pg;
 id |   value    
----+------------
  1 | PostgreSQL
(1 row)
```
*执行失败*
Oracle数据表添加唯一索引，插入会失败。
```
TEST-orcl@DESKTOP-V430TU3>alter table t_oracle add primary key(id);
Table altered.
```
Java日志输出
```
---------- PG -----------
---------- PG -----------
---------- Oracle -----------
ORA-00001: 违反唯一约束条件 (TEST.SYS_C0064492)
---------- DONE -----------
```
查询PG数据库
```
[local:/data/run/pg12]:5120 pg12@testdb=# select * from t_pg;
 id |   value    
----+------------
  1 | PostgreSQL
(1 row)

```
仍然是1条记录，实现了跨数据库的事务一致性。
**参考资料**
[ Prepared Transactions in PostgreSQL 9.2 ](http://chirupgadmin.blogspot.com/2013/05/prepared-transactions-in-postgresql.html)
[PREPARE TRANSACTION](http://www.postgres.cn/docs/11/sql-prepare-transaction.html)