Use mysql_fdw to read and write MySQL data

Procedure

1. Create the mysql_fdw plug-in.

   postgres=> create extension mysql_fdw;  
   CREATE EXTENSION  

2. Create a MySQL server.

   postgres=> CREATE SERVER <The name to use for the MySQL server>  
   postgres->      FOREIGN DATA WRAPPER mysql_fdw
   postgres->      OPTIONS (host '<The endpoint to connect the MySQL server>', port '<The port to connect the MySQL server>');  
   CREATE SERVER  

   Example:

   postgres=> CREATE SERVER mysql_server  
   postgres->      FOREIGN DATA WRAPPER mysql_fdw
   postgres->      OPTIONS (host 'rm-xxx.mysql.rds.aliyuncs.com', port '3306');  
   CREATE SERVER  

3. Map the MySQL server to an account created in your ApsaraDB RDS PostgreSQL instance. That account is used to read and write data to the target MySQL database on the MySQL server.

   postgres=> CREATE USER MAPPING FOR <The username of the account to which the MySQL server is mapped>   
   SERVER <The name of the MySQL server>  
   OPTIONS (username '<The username for logging on to the target MySQL database>', password '<The password for logging on to the target MySQL database>');  
   CREATE USER MAPPING  

   Example:

   postgres=> CREATE USER MAPPING FOR pgtest 
   SERVER mysql_server  
   OPTIONS (username 'mysqltest', password 'Test1234!') ;  
   CREATE USER MAPPING  

4. Create a foreign MySQL table by using the account that you mapped to the MySQL server in the previous step.
   Note The field names in the foreign MySQL table must be the same as those in the target table of the target MySQL database. You have the option to create only the fields you want to query. For example, if the target table in the target MySQL database contains three fields, ID, NAME, and AGE, you have the option to create only two fields, ID and NAME, in the foreign MySQL table.

   postgres=> CREATE FOREIGN TABLE <The name to use for the foreign MySQL table> (<The name of field 1> <The data type of field 1>,<The name of field 2> <The data type of field 2>...) server <The name of the MySQL server> options (dbname '<The name of the target MySQL database>', table_name '<The name of the target table in the target MySQL database>');  
   CREATE FOREIGN TABLE  

   Example:

   postgres=> CREATE FOREIGN TABLE ft_test (id1 int, name1 text) server mysql_server options (dbname 'test123', table_name 'test');  
   CREATE FOREIGN TABLE  

What to do next

You can use the foreign MySQL table to test the performance of reading and writing data to the target MySQL database.

ERROR:  first column of remote table must be unique for INSERT/UPDATE/DELETE operation.

postgres=> select * from ft_test ;  

postgres=> insert into ft_test values (2,'abc');  
INSERT 0 1  

postgres=> insert into ft_test select generate_series(3,100),'abc';  
INSERT 0 98  
postgres=> select count(*) from ft_test ;  
 count   
-------  
    99  
(1 row)  

Check the execution plan to find out how the requests sent from your ApsaraDB RDS PostgreSQL instance to query data from the target MySQL database are executed.

postgres=> explain verbose select count(*) from ft_test ;  
                                  QUERY PLAN                                     
-------------------------------------------------------------------------------  
 Aggregate  (cost=1027.50..1027.51 rows=1 width=8)  
   Output: count(*)  
   ->  Foreign Scan on public.ft_test  (cost=25.00..1025.00 rows=1000 width=0)  
         Output: id, info  
         Remote server startup cost: 25  
         Remote query: SELECT NULL FROM `test123`.`test`  
(6 rows)  

postgres=> explain verbose select id from ft_test where id=2;  
                               QUERY PLAN                                  
-------------------------------------------------------------------------  
 Foreign Scan on public.ft_test  (cost=25.00..1025.00 rows=1000 width=4)  
   Output: id  
   Remote server startup cost: 25  
   Remote query: SELECT `id` FROM `test123`.`test` WHERE ((`id` = 2))  
(4 rows)