Contents

• MySQL Foreign Data Wrapper for PostgreSQL
  • 1. Installation
  • Enhancements
    • Write-able FDW
    • Connection Pooling
    • Where clause push-down
    • Column push-down
    • Prepared Statment
  • Usage
  • Contributing
  • Support
  • Changelog
  • Version 2.1.0
  • License

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 only works with PostgreSQL Version 9.3 and greater, for previous version support please download from PG_92 branch.

We have added a number of significant enhancements to the mysql fdw, some of the major enhancements are listed in the “enhancements” section of this document.

1. 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

Not that we have tested the mysql_fdw extension only on MacOS and Ubuntu systems, but other *NIX's should also work.

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 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 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 Statment

(Refactoring for select queries to use prepared statement)

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

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 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.

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.

-- 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 datetime)
SERVER mysql_server
     OPTIONS (dbname 'db', table_name 'warehouse');

-- insert new rows in table

INSERT INTO warehouse values (1, 'UPS', sysdate());
INSERT INTO warehouse values (2, 'TV', sysdate());
INSERT INTO warehouse values (3, 'Table', sysdate());

-- select from table

SELECT * FROM warehouse;

warehouse_id | warehouse_name | warehouse_created  

--------------+----------------+--------------------

        1 | UPS            | 29-SEP-14 23:33:46

        2 | TV             | 29-SEP-14 23:34:25

        3 | Table          | 29-SEP-14 23:33:49

-- 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

EXPLAIN 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)
->  Foreign Scan on warehouse  (cost=10.00..13.00 rows=3 width=36)
     Local server startup cost: 10
     Remote query: SELECT warehouse_id, warehouse_name FROM db.warehouse WHERE ((warehouse_name like 'TV'))

Planning time: 0.564 ms (5 rows)

Contributing

If you experince 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 guidlines.

Support

This project will be modified to maintain compatibility with new PostgreSQL releases.

As with many open source projects, you may be able to obtain support via the public mailing list (mysql_fdw @ enterprisedb.com). If you require commercial support, please contact the EnterpriseDB sales team, or check whether your existing PostgreSQL support provider can also support mysql_fdw.

Changelog

Version 2.1.0

The following features are added as part of this mysql_fdw release :

1) Support for PostgreSQL 9.5.

2) IMPORT FOREIGN SCHEMA support. Now mysql_fdw can use the import foreign schema functionality to import the remote server schema metadata in PostgreSQL. (pull request #62)

3) DML support for binary data. Binary data (longblob) in MySQL can mapped to PostgreSQL's bytea datatype. (#66)

4) Support and map the MySQL datatype 'mediumblob' to BYTEA in PostgreSQL. (pull request #82)

5) Support for JSON data type. (#58)

6) Added MariaDB client library compatibility. (pull request #59)

7) Added init_command server option which is used as MYSQL_INIT_COMMAND and may be used as OPTION in CREATE SERVER statement.

8) Introduced new server option "use_remote_estimate". (#75)

A new foreign server option "use_remote_estimate" is added. If this option is true for a server then server gets the number of rows from remote MySQL server. Server issues an "EXPLAIN" call for the query to remote MySQL server and gets the rows column and filtered column. Using the rows and filtered column, it calculates the actual number of rows for the query.

9) Adding mysql regression's init script.

10) Script create database and all the required table in MySQL's database. Script need to be run before running the regression.

11) Enable / Disable secure authentication by using MYSQL option flag MYSQL_SECURE_AUTH. By default secure authentication is true. This option is added for legacy systems which does not support secure authentication. (#39)

The following bug fixes are done as part of this mysql_fdw release:

1) Fix IMPORT FOREIGN SCHEMA issues with LIMIT/EXCLUDE (pull request #84)

2) Wrapped table names for LIMIT/EXCLUDE in single quotes so these keywords can be used as table names.

3) Modified foreign schema query to use null-safe equals operator

4) Don't send "E" for regular expression. This is needed so regular expressions can work properly. (#77)

5) Builtin functions have different names in PostgreSQL and MySQL. Current implementation is for translating PostgreSQL's btrim to MySQL' trim. To do the translation mysql_deparse_func_expr function performs the replacement. (#70)

6) Don't quote functions in WHERE clause while push down to remote server. The mysql server doesn't execute them as a function if they functions names are quoted. (#42)

7) Don't push WHERE clause in case of PARAM value. Since the param values are not available at the remote server, this ends up causing an error. (#44)

8) Added a check, that forces that the first column of MySQL table must have a unique constraint. (#45)

9) Improvements to pattern matching algorithm

License

Copyright (c) 2011 - 2014, 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.