mysql同步数据到PostgreSQL(使用mysql_fdw)

1、安装
下载地址：https://github.com/EnterpriseDB/mysql_fdw

修改环境变量：

export MYSQLHOME=/usr/local/mysql  
export PGHOME=/home/pg12/pgsql12.4  
export LD_LIBRARY_PATH=$PGHOME/lib:$MYSQLHOME/lib:/lib64:/usr/lib64:/usr/local/lib64:/lib:/usr/lib:/usr/local/lib  
export PATH=$PGHOME/bin:$MYSQLHOME/bin:$PATH:.  

解压安装：
[root@oracle ~]# unzip mysql_fdw-master.zip
[root@oracle ~]# cd mysql_fdw-master
[root@oracle ~]# make USE_PGXS=1
[root@oracle ~]# make USE_PGXS=1 install

在pg中创建mysql_fdw插件：

bill=# create extension mysql_fdw ;
CREATE EXTENSION

这一步可能会出现如下报错：

bill=# create extension mysql_fdw ;
ERROR:  failed to load the mysql query: 
libmysqlclient.so: cannot open shared object file: No such file or directory
HINT:  export LD_LIBRARY_PATH to locate the library

如果是源码编译安装的MySQL可能会出现这个问题，需要设置LD_LIBRARY_PATH，设置完之后再重新启动pg数据库。

2、使用
mysql中测试表：

mysql> select * from t_mysql;
+------+---------------+
| id   | info          |
+------+---------------+
|    1 | this is mysql |
+------+---------------+
1 row in set (0.00 sec)

pg中创建对应的forein server和外部表：

bill=# CREATE SERVER mysql_server
bill-#      FOREIGN DATA WRAPPER mysql_fdw
bill-#      OPTIONS (host '127.0.0.1', port '3306');
CREATE SERVER

bill=# CREATE USER MAPPING FOR bill
bill-# SERVER mysql_server
bill-# OPTIONS (username 'root', password 'root.123');
CREATE USER MAPPING

bill=# CREATE FOREIGN TABLE mysql_foreign_table1(
bill(#      id int,
bill(#      info text)
bill-# SERVER mysql_server
bill-#      OPTIONS (dbname 'bill', table_name 't_mysql');
CREATE FOREIGN TABLE

查看：
数据已经同步过来

bill=# select * from mysql_foreign_table1 ;
 id |     info      
----+---------------
  1 | this is mysql
(1 row)

我们还可以直接IMPORT整个库生成本地的外部表。
例如：

bill=# IMPORT FOREIGN SCHEMA bill FROM SERVER mysql_server into bill;
IMPORT FOREIGN SCHEMA

可以发现，mysql中所有表都import过来了：

bill=# \dE
                   List of relations
 Schema |         Name         |     Type      | Owner 
--------+----------------------+---------------+-------
 bill   | mysql_foreign_table1 | foreign table | bill
 bill   | t_mysql              | foreign table | bill
 bill   | test                 | foreign table | bill
(3 rows)

写入数据：
我们可以直接在pg中写数据到mysql数据库，但是mysql的表必须有主键才可以：

bill=# insert into mysql_foreign_table1 values(2,'this is postgres');
ERROR:  first column of remote table must be unique for INSERT/UPDATE/DELETE operation

在mysql中添加主键：

mysql> alter table t_mysql add primary key(id);
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

再次插入就可以成功了：

bill=# insert into mysql_foreign_table1 values(2,'this is postgres');
INSERT 0 1

我们还可以查看在pg中查询mysql中的表的执行计划会是什么样的：

bill=# explain verbose select count(*) from mysql_foreign_table1 ;
                                        QUERY PLAN                                        
------------------------------------------------------------------------------------------
 Aggregate  (cost=1012.50..1012.51 rows=1 width=8)
   Output: count(*)
   ->  Foreign Scan on bill.mysql_foreign_table1  (cost=10.00..1010.00 rows=1000 width=0)
         Output: id, info
         Local server startup cost: 10
         Remote query: SELECT NULL FROM `bill`.`t_mysql`
(6 rows)

bill=# explain verbose select * from mysql_foreign_table1 where id=1;
                                     QUERY PLAN                                      
-------------------------------------------------------------------------------------
 Foreign Scan on bill.mysql_foreign_table1  (cost=10.00..1010.00 rows=1000 width=36)
   Output: id, info
   Local server startup cost: 10
   Remote query: SELECT `id`, `info` FROM `bill`.`t_mysql` WHERE ((`id` = 1))
(4 rows)