MySQL Foreign Data Wrapper for PostgreSQL

This PostgreSQL extension implements a Foreign Data Wrapper (FDW) for MySQL.

Please note that this version of mysql_fdw works with PostgreSQL and EDB Postgres Advanced Server 12, 13, 14, 15, and 16.

Installation

To compile the MySQL foreign data wrapper, MySQL's C client library is needed. This library can be downloaded from the official MySQL website.

1. To build on POSIX-compliant systems you need to ensure the pg_config executable is in your path when you run make. This executable is typically in your PostgreSQL installation's bin directory. For example:

   $ export PATH=/usr/local/pgsql/bin/:$PATH
   

2. The mysql_config must also be in the path, it resides in the MySQL bin directory.

   $ export PATH=/usr/local/mysql/bin/:$PATH
   

3. Compile the code using make.

   $ make USE_PGXS=1
   

4. Finally install the foreign data wrapper.

   $ make USE_PGXS=1 install
   

5. Running regression test.

   $ make USE_PGXS=1 installcheck
   

   However, make sure to set the MYSQL_HOST, MYSQL_PORT, MYSQL_USER_NAME, and MYSQL_PWD environment variables correctly. The default settings can be found in the mysql_init.sh script.

If you run into any issues, please let us know.

Enhancements

The following enhancements are added to the latest version of mysql_fdw:

Write-able FDW

The previous version was only read-only, the latest version provides the write capability. The user can now issue an insert, update, and delete statements for the foreign tables using the mysql_fdw. It uses the PG type casting mechanism to provide opposite type casting between MySQL and PG data types.

Connection Pooling

The latest version comes with a connection pooler that utilises the same MySQL database connection for all the queries in the same session. The previous version would open a new MySQL database connection for every query. This is a performance enhancement.

WHERE clause push-down

The latest version will push-down the foreign table where clause to the foreign server. The where condition on the foreign table will be executed on the foreign server hence there will be fewer rows to bring across to PostgreSQL. This is a performance feature.

Column push-down

The previous version was fetching all the columns from the target foreign table. The latest version does the column push-down and only brings back the columns that are part of the select target list. This is a performance feature.

Prepared Statement

(Refactoring for select queries to use prepared statement)

The select queries are now using prepared statements instead of simple query protocol.

JOIN push-down

mysql_fdw now also supports join push-down. The joins between two foreign tables from the same remote MySQL server are pushed to a remote server, instead of fetching all the rows for both the tables and performing a join locally, thereby enhancing the performance. Currently, joins involving only relational and arithmetic operators in join-clauses are pushed down to avoid any potential join failure. Also, only the INNER and LEFT/RIGHT OUTER joins are supported, and not the FULL OUTER, SEMI, and ANTI join. This is a performance feature.

AGGREGATE push-down

mysql_fdw now also supports aggregate push-down. Push aggregates to the remote MySQL server instead of fetching all of the rows and aggregating them locally. This gives a very good performance boost for the cases where aggregates can be pushed down. The push-down is currently limited to aggregate functions min, max, sum, avg, and count, to avoid pushing down the functions that are not present on the MySQL server. Also, aggregate filters and orders are not pushed down.

ORDER BY push-down

mysql_fdw now also supports order by push-down. If possible, push order by clause to the remote server so that we get the ordered result set from the foreign server itself. It might help us to have an efficient merge join. NULLs behavior is opposite on the MySQL server. Thus to get an equivalent result, we add the "expression IS NULL" clause at the beginning of each of the ORDER BY expressions.

LIMIT OFFSET push-down

mysql_fdw now also supports limit offset push-down. Wherever possible, perform LIMIT and OFFSET operations on the remote server. This reduces network traffic between local PostgreSQL and remote MySQL servers. ALL/NULL options are not supported on the MySQL server, and thus they are not pushed down. Also, OFFSET without LIMIT is not supported on the MySQL server hence queries having that construct are not pushed.

Usage

The following parameters can be set on a MySQL foreign server object:

• host: Address or hostname of the MySQL server. Defaults to 127.0.0.1
• port: Port number of the MySQL server. Defaults to 3306
• secure_auth: Enable or disable secure authentication. Default is true
• init_command: SQL statement to execute when connecting to the MySQL server.
• use_remote_estimate: Controls whether mysql_fdw issues remote EXPLAIN commands to obtain cost estimates. Default is false
• reconnect: Enable or disable automatic reconnection to the MySQL server if the existing connection is found to have been lost. Default is false.
• sql_mode: Set MySQL sql_mode for established connection. Default is ANSI_QUOTES.
• ssl_key: The path name of the client private key file.
• ssl_cert: The path name of the client public key certificate file.
• ssl_ca: The path name of the Certificate Authority (CA) certificate file. This option, if used, must specify the same certificate used by the server.
• ssl_capath: The path name of the directory that contains trusted SSL CA certificate files.
• ssl_cipher: The list of permissible ciphers for SSL encryption.
• fetch_size: This option specifies the number of rows mysql_fdw should get in each fetch operation. It can be specified for a foreign table or a foreign server. The option specified on a table overrides an option specified for the server. The default is 100.
• character_set: The character set to use for MySQL connection. Default is auto which means autodetect based on the operating system setting. Before the introduction of the character_set option, the character set was set similar to the PostgreSQL database encoding. To get this older behavior set the character_set to special value PGDatabaseEncoding.
• mysql_default_file: Set the MySQL default file path if connection details, such as username, password, etc., need to be picked from the default file.

The following parameters can be set on a MySQL foreign table object:

• dbname: Name of the MySQL database to query. This is a mandatory option.
• table_name: Name of the MySQL table, default is the same as foreign table.
• max_blob_size: Max blob size to read without truncation.
• fetch_size: Same as fetch_size parameter for foreign server.

The following parameters need to supplied while creating user mapping.

• username: Username to use when connecting to MySQL.
• password: Password to authenticate to the MySQL server with.

The following parameters can be set on IMPORT FOREIGN SCHEMA command:

• import_default: This option controls whether column DEFAULT expressions are included in the definitions of foreign tables imported from a foreign server. The default is false.
• import_not_null: This option controls whether column NOT NULL constraints are included in the definitions of foreign tables imported from a foreign server. The default is true.
• import_enum_as_text: This option can be used to map MySQL ENUM type to TEXT type in the definitions of foreign tables, otherwise emit a warning for type to be created. The default is false.
• import_generated: This option controls whether GENERATED column expressions are included in the definitions of foreign tables imported from a foreign server or not. The default is true. The IMPORT will fail altogether if an imported generated expression uses a function or operator that does not exist on PostgreSQL.

Examples

-- load extension first time after install
CREATE EXTENSION mysql_fdw;

-- create server object
CREATE SERVER mysql_server
	FOREIGN DATA WRAPPER mysql_fdw
	OPTIONS (host '127.0.0.1', port '3306');

-- create user mapping
CREATE USER MAPPING FOR postgres
	SERVER mysql_server
	OPTIONS (username 'foo', password 'bar');

-- create foreign table
CREATE FOREIGN TABLE warehouse
	(
		warehouse_id int,
		warehouse_name text,
		warehouse_created timestamp
	)
	SERVER mysql_server
	OPTIONS (dbname 'db', table_name 'warehouse');

-- insert new rows in table
INSERT INTO warehouse values (1, 'UPS', current_date);
INSERT INTO warehouse values (2, 'TV', current_date);
INSERT INTO warehouse values (3, 'Table', current_date);

-- select from table
SELECT * FROM warehouse ORDER BY 1;

warehouse_id | warehouse_name | warehouse_created
-------------+----------------+-------------------
           1 | UPS            | 10-JUL-20 00:00:00
           2 | TV             | 10-JUL-20 00:00:00
           3 | Table          | 10-JUL-20 00:00:00

-- delete row from table
DELETE FROM warehouse where warehouse_id = 3;

-- update a row of table
UPDATE warehouse set warehouse_name = 'UPS_NEW' where warehouse_id = 1;

-- explain a table with verbose option
EXPLAIN VERBOSE SELECT warehouse_id, warehouse_name FROM warehouse WHERE warehouse_name LIKE 'TV' limit 1;

                                   QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
Limit  (cost=10.00..11.00 rows=1 width=36)
	Output: warehouse_id, warehouse_name
	->  Foreign Scan on public.warehouse  (cost=10.00..1010.00 rows=1000 width=36)
		Output: warehouse_id, warehouse_name
		Local server startup cost: 10
		Remote query: SELECT `warehouse_id`, `warehouse_name` FROM `db`.`warehouse` WHERE ((`warehouse_name` LIKE BINARY 'TV'))

For more details, please refer to mysql_fdw documentation.

Contributing

If you experience any bug and have a fix for that, or have a new idea, create a ticket on github page. Before creating a pull request please read the contributing guidelines.

Support

This project will be modified to maintain compatibility with new PostgreSQL and EDB Postgres Advanced Server releases.

If you require commercial support, please contact the EnterpriseDB sales team, or check whether your existing PostgreSQL support provider can also support mysql_fdw.

License

Copyright (c) 2011-2024, EnterpriseDB Corporation.

Permission to use, copy, modify, and distribute this software and its documentation for any purpose, without fee, and without a written agreement is hereby granted, provided that the above copyright notice and this paragraph and the following two paragraphs appear in all copies.

See the LICENSE file for full details.