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To use this driver, see the Samples further down in this README document.

Emysql implements a stable driver toward the MySQL database. It currently support fairly recent versions (somewhere around 5.3+) and it is considered fairly stable in production.

The driver has several technical shortcomings:

  • No clear protocol / connection pool separation
  • No clear protocol / socket separation
  • A very complicated connection pool management
  • Uses the textual protocol in a lot of places where it shouldthe binary protocol
  • The API could be better

However, this is probably the best MySQL driver out there for Erlang. The erlang-mysql-driver uses a problematic connection pool design for many use cases and is not suitable for general purpose use. This driver is.


Semantic versioning is used. Versions are given as x.y.z:

  • x changes break backward compatibility
  • y changes add new functionality—but does not break compatibility backwards
  • z changes recognizes a new version, but is not supposed to break anything

Changelog of recent changes

Emysql 0.4.1

Spring cleaning in the repository:

  • Removed a lot of modules which is not part of the official API from the documentation.
  • Deprecated the use of emysql_util for emysql.
  • Made tests actually do something with the emysql_util calls.
  • Moved function calls from emysql_util into the modules where they belong.

Change should be backwards compatible.

Emysql 0.4.0

Introduced changes by Garrett Smith:

  • Support connection timeouts in gen_tcp:connect/3. This allows the driver to better handle connection timeouts upon initial connections.
  • Introduce emysql:add_pool/2 as a proplist-based way of initializing a pool. This is going to be the preferred way of initializing pools in the future.

Emysql 0.3.2

  • We should be on Travis CI now with full tests running
  • Pulled in lots of smaller changes which should be rather cosmetic fixes.
  • R16 warnings eliminated (Jesse Gumm)
  • Tried to consolidate simple parts of the driver

Emysql 0.3.0

Note: Automatic conversion to the encoding of the underlying MySQL server was removed in the 0.3.x branch. If you specify, e.g., utf-8 encoding, then the MySQL server will reject wrongly-encoded strings and data, but the driver will not perform any encoding by itself anymore.

It is now the driver callers responsibility to ensure that data is properly encoded. This change makes it possible to pass binary BLOB data to the MySQL server once again.


This is an Erlang MySQL driver, based on a rewrite at Electronic Arts. Easy to use, strong connection pooling, prepared statements & stored procedures. Optimized for a central node architecture and OLTP.

While you can use mysql via ODBC, you should see better performance when using a driver like Emysql. For samples and docs see below. Read the brief on choosing a package and about the history of the various MySQL drivers.

Emysql is a cleaner rewrite of erlang-mysql-driver, see History. This fork is a direct continuation of the original emysql with fixes, updates, more documentation and samples.

This is the master branch. Should you run into problems, please report them by opening an issue at github and try if they go away by checking out the 'stable' branch. Thank you.

Which fork/package should I use? Likely this one, but see Choosing. Why are there so many? See History. Who used this fork? Electronic Arts. How do I ...? See Samples. Hello ...? See Samples.

Download: Docs: Issues: Repository:




In most cases, especially for high performance and stability, this package, Emysql, will be the best choice. It was rewritten from the ground up to overcome fundamental issues of 'erlang-mysql-driver'. It also has some usable docs meanwhile.


If you are looking for the plain necessities, you should use the ejabberd mysql driver. It is simple, battle tested and stable. There are comprehensive instructions in the source comments.


This driver currently does not support transactions.

For mnesia-style transactions, one of the multiple 'erlang-mysql-drivers' may suite you best. There are quite many branches of it out there, and they are based on the same project as the ejabberd driver. To learn more about out the differences between the drivers, see the mysql driver history.


Hello World

This is a hello world program. Follow the three steps below to try it out.


run() ->


        emysql:add_pool(hello_pool, [{size,1},

                <<"INSERT INTO hello_table SET hello_text = 'Hello World!'">>),

        Result = emysql:execute(hello_pool,
                <<"select hello_text from hello_table">>),

        io:format("~n~p~n", [Result]).

We'll be coming back to this source to make it run on your machine in a minute. But let's look at the basic building blocks first:

Executing an SQL Statement

emysql:execute(my_pool, <<"SELECT * from mytable">>).

For the exact spec, see below, Usage. Regarding the 'pool', also see below.

Executing a Prepared Statement

emysql:prepare(my_stmt, <<"SELECT * from mytable WHERE id = ?">>).

emysql:execute(my_pool, my_stmt, [1]).

Executing Stored Procedures

emysql:execute(my_pool, <<"create procedure my_sp() begin select * from mytable; end">>).

emysql:execute(my_pool, <<"call my_sp();">>).

Result Record

-record(result_packet, {seq_num, field_list, rows, extra}).

Converting Row Data To Records

-record(foo, {bar, baz}).

Result = emysql:execute(pool1, <<"select bar, baz from foo">>).
Recs = emysql:as_record(Result, foo, record_info(fields, foo)).
Bars = [ || Foo <- Recs].

Adding a Connection to the Connection Pool

Emysql uses a sophisticated connection pooling mechanism.

emysql:add_pool(my_pool, [{size,1}, {user,"myuser"}, {password,"mypass"},
        {host,"myhost"}, {port,3306},{database,"mydatabase"}, {encoding,utf8}]).

Arbitrary post-connection start-up commands can be added with the proplist key atom start_cmds:

emysql:add_pool(my_pool, [{size,1}, {user,"myuser"}, {password,"mypass"},
        {host,"myhost"}, {port,3306},{database,"mydatabase"}, {encoding,utf8},
                <<"SET TIME_ZONE='+00:00'">>,
                <<"SET SQL_MODE='STRICT_ALL_TABLES'">>

Running Hello World

Let's run the hello world sample from above:

1. Build Emysql

Build, using make:

$ cd Emysql
$ make

Or use rebar:

$ cd Emysql
$ ./rebar compile

Both yield an option to install but this is not needed for the samples.

2. Make a Sample Database

For use in the above sample (and all of those below, too), create a local mysql database. You should have a mysql server installed and running:

$ mysql [-u<user> -p]
mysql> create database hello_database;
mysql> use hello_database;
mysql> create table hello_table (hello_text char(20));
mysql> grant all privileges on hello_database.* to hello_username@localhost identified by 'hello_password';

3. Paste & Run Hello

Be sure to have ./ebin in your Erlang path. The hello-world source as shown above already waits in the Emysql directory, as hello.erl. Just compile and run it:

$ erlc hello.erl
$ erl -pa ./ebin -s hello run -s init stop -noshell

That's it. If you need to blindly repeat that more often some time, you can also use

$ make hello

There are more sample programs:

More Samples

Sample programs are in ./samples.

To run the samples, create the database as listed above at localhost, and simply run the compile & run batches:

$ cd samples
$ ./a_hello
$ ./b_raw
$ ./c_rows_as_records
$ ./d_prepared_statement
$ ./e_stored_procedure
$ ./f_load_from_file
$ ./g_rows_as_json

or (after building and the database, as explained above), start a_hello etc. manually along these lines:

$ make
$ cd samples
$ erlc a_hello.erl
$ erl -pa ../ebin -s a_hello run -s init stop -noshell


General Notes on using Emysql, including the actual specs:

Starting an Application

The Emysql driver is an Erlang gen-server, and, application.

crypto:start(), % Only needed for testing. In a proper release, this would happen automatically

Adding a Pool

To add a pool, use emysql:add_pool/2 which takes a proplist of parameters. If you need to use one of the emysql:add_pool/K variants, please be aware that they are deprecated in favor of add_pool/2 and will be removed in a future version. See the documentation for what options the add_pool call accepts.

More Record Types

Emysql usually operates with a number of different record types from the database. The driver returns "raw" responses as "packets" and leaves it up to the calling application to handle the result, usually by using one of the conversion routines in emysql to turn the data into a more suitable format.

-record(result_packet, {seq_num, field_list, rows, extra}).

-record(ok_packet, {seq_num, affected_rows, insert_id, status, warning_count, msg}).

-record(error_packet, {seq_num, code, msg}).

For other record types, see include/emysql.hrl.

Executing SQL Statements

% emysql:execute(PoolName, Statement) -> result_packet() | ok_packet() | error_packet()
% PoolName = atom()
% Statement = string() | binary()

emysql:execute(mypoolname, <<"SELECT * from mytable">>).
# result_packet{field_list=[...], rows=[...]}

emysql:execute(mypoolname, <<"UPDATE mytable SET bar = 'baz' WHERE id = 1">>).
# ok_packet{affected_rows=1}

Executing Prepared Statements

	% emysql:prepare(StmtName, Statement) -> ok
	% StmtName = atom()
	% Statement = binary() | string()
	emysql:prepare(my_stmt, <<"SELECT * from mytable WHERE id = ?">>).
	# ok

	% emysql:execute(PoolName, StmtName, Args) -> result_packet() | ok_packet() | error_packet()
	% StmtName = atom()
	% Args = [term()]
	emysql:execute(mypoolname, my_stmt, [1]).
	#result_packet{field_list=[...], rows=[...]}

Executing Stored Procedures

% emysql:execute(PoolName, StmtName, Args) -> result_packet() | ok_packet() | error_packet()
% StmtName = atom()
% Args = [term()]

	<<"create procedure sp_hello() begin select * from hello_table; end">>).

emysql:execute(hello_pool, <<"call sp_hello();">>).
                [[<<"Hello World!">>],[<<"Hello World!">>]],

Note that you are getting back a list of results here.

Converting Row Data To Records

% emysql:as_record(ResultPacket, RecordName, Fields) -> Result
% ResultPacket = result_packet()
% RecordName = atom() (the name of the record to generate)
% Fields = [atom()] (the field names to generate for each record)
% Result = [record()]

-record(foo, {bar, baz, bat}).

fetch_foo() ->
        Result = emysql:execute(pool1, <<"select bar, baz, bat from foo">>),
        Recs = emysql:as_record(Result, foo, record_info(fields, foo)),
                io:format("foo: ~p, ~p, ~p~n", [, Foo#foo.baz, Foo#foo.bat])
         end || Foo <- Recs].

Converting Row Data To JSON

% emysql:as_json(ResultPacket) -> Result
% Result = [json()]

Result = emysql:execute(pool1, <<"select bar, baz from foo">>),

JSON = emysql:as_json(Result).
% [[{<<"bar">>,<<"bar_value">>}, {<<"baz">>,<<"baz_value">>}], ...]

Note that you are getting back a list of erlang terms in accordance with EEP-18. For actual utf8 binary JSON string you will need external library like jsx or jiffy

Loading Data From a File

        <<"LOAD DATA INFILE 'hello.txt' INTO TABLE hello_table (hello_text)">>).

Note, you must grant:

grant file on *.* to hello_username@localhost identified by'hello_password';

You need to give LOCAL or an absolute path, else the file is expected in the database server root. To use the current directory:

{ok, Dir} = file:get_cwd(),
    list_to_binary("LOAD DATA INFILE '" ++ Dir ++
        "/hello.txt' INTO TABLE hello_table (hello_text)")).


Please add a Common Test suite if you are proposing a pull request!

Basic Tests

Some Common Tests (Unit Tests) have been added in the test folder. They have no significant coverage yet but can help to test the basics. They might also help you find trip ups in your system set up (environment and basics suites).

For the basic tests you only need the test database set up and a mysql server running, the same as described above for the samples:

$ mysql [-u<user> -p]
mysql> create database hello_database;
mysql> use hello_database;
mysql> create table hello_table (hello_text char(20));
mysql> grant all privileges on hello_database.* to hello_username@localhost identified by 'hello_password';

To run the basic tests, at the command line type:

make test

Some tests can take up to half a minute to finish on a slow machine.

These tests currently check access to the database (environment suite) the same functionality as the samples (basics suite) and for race conditions as described in issue #9. Thank you, Ransom!

To look at the tests, open logs/index.html in a browser:

open logs/index.html # Will work on a Mac for instance


Open Source Erlang MySQL driver efforts are a fractured matter. You may find yourself digging in the sources to find out about their relationships with each other - and which one to pick. Here is a brief history.

Yxa: The first Erlang MySQL driver, in ~270 lines of code, seems to have been written between 2001 and 2004 by Magnus Ahltorp at the Swedish Royal Institute of Technology. It exposes low level, blocking functions to talk 4.0 protocol with a MySQL server. In 2005 Fredrik Thulin brought the driver into its current modular form to use it for the the SIP proxy Yxa while working at the Stockholm University. It has three process layers: a high level, round-robin connection pooling module; then, middle-man, single-connection, blocking processes that do the bit-level wrangling with the MySQL protocol. This module, mysql_conn, can also be used as a single-connection, stand-alone driver. And below this, there are small, protocol-agnostic receiver processes that handle the socket communication with the server, no matter the contents. Fredrik implemented gen-server behavior, added logging, error messages, upgraded authentication, and thoroughly commented the source. This mysql driver is working, complete and stable since at least 2007, it is available as part of Yxa 1.0 (hosted on github). It has no support for transactions or stored procedures. It is the basis for the following two packages. Its basic modular division and general functionality were not changed but only enhanced and it had originally been agreed upon that the Yxa branch should receive and merge the contributions of the later forks upstream. Unfortunately, that did not come to pass.

ejabberd: In 2006, a fork of the Yxa driver was created by Mickael Remond at Process One to become part of the successful instant messaging server ejabberd (also hosted on github). It can be assumed to be as stable as the Yxa branch, didn't change a byte in the lowest level, but only slightly enhanced the higher level. The difference from the original Yxa branch consists mainly of added inspection functions that help using the query results, and of an independent adoption of the MySQL 4.1 client-server protocol. The original Yxa branch has meanwhile adopted EDoc comment format, which makes the sources look more different than they actually are. You can find a Jan 2011 diff between Yxa and the ejabberd version here, and one ignoring comments here. These two branches could be merged quite easily, probably without any change in functionality at all.

erlang-mysql-driver: The storied life of this branch began in 2006 when Yariv Sadan created a fork from the ejabberd branch, made it a standalone project, gave it the maximally generic name that stuck, and hosted it on Google Code. Before he moved on to work at Facebook, he added high-level handling of prepared statements and transactions, and at long last completed some loose ends with the connection pooling that had been known to be lagging since the Yxa version. There were changes both in the original Yxa and the ejabberd branch after the forking off that never made their way into this fork, but in all likelihood they must be minor. It is not always obvious if the changes in erlang-mysql-driver had reached their intended final form. The separation of the three process layers seems to have suffered and complicated enhancements as the highest layer module, mysql.erl, started to become entangled with the second, mysql_conn.erl. Maybe that had a part in why the upstream merge never happened. The main repository of this fork lay dormant since Oct '07 when in Feb '10, Dave Smith, the rebar guy, started making some updates and put them on github. The driver is now enjoying a couple of active forks that make a convincing case for the github Network graphs.

A parallel fork from Yariv's branch, not entangled with Dave's tree, is the one by Nick Gerakines. I suspect it could technically be the strongest of the erlang-mysql-driver forks, with a lot of clean up work by smart guys put in, although it is generally less well known. And much less forked. In the end, the branch was abandoned for Emysql. In all branches, documentation beyond the source comments remains lacking.

Emysql was created from scratch in 2009, specifically to achieve better stability and throughput. It was proposed and written by Jacob Vorreuter at Electronic Arts and deployed at Shawn Fanning's, a social network site for gamers. Initially, Nick Gerakines, Jacob's boss at EA, rewrote large parts of erlang-mysql-server to clean it up. But some fundamental problems remained and when half a year in, they still could not overcome performance and stability issues, Nick gave Jacob the green light to rewrite it from the ground up because they felt that, in Jacob's words, the Yxa branch had been touched by so many people that it had become more complicated than necessary. According to Jacob, Bill Warnecke helped in the early design and testing. They abandoned the separation into three process layers and pulled the socket handling and bit-parsing into one module, coupling the functionality into direct function calls. It looks like they borrowed some chore lines from Magnus but generally created a new, straightforward architecture focused on providing a high performance node. Not only can Emysql open multiple connections, but multiple pools of multiple connections each to multiple database servers, which makes for a strong central OLTP node. Jacob says that Emysql is pretty stable and ran without issues in production at EA. Nick remembers: "The primary way we used it was to have a single Erlang node be the MySQL communication point and allow a number of connected nodes to connect through it to MySQL. We wanted very high throughput with many pids across a grid connecting to it and needed the ability to have a number of MySQL connections open for connection pooling." Rupture was killed in the consolidations of 2009. But Shawn could probably keep the money and we the fond memory of Napster and now, the glistening Emysql.

Eonblast Emysql is a continuation fork of Jacob's work, including all his commits and adding docs, samples, fixes and extensions. Henning Diedrich, Vitaliy Batichko, Chris Rempel, Patrick Atambo, Joel Meyer, Erik Seres, Alexey Lebedeff, Logan Owen, Seven Du, Brendon Hogger, Bart van Deenen, Ransom Richardson and Qing Liang have contributed to this branch. Support for stored procedures has been added, remaining issues are being addressed and there is work going on to bring Mnesia-style transactions. The fork is still close to the original, which currently lies dormant, but has started to add features and possibly increased stability.

Fredrik, Nick and Jacob helped shedding light on the matter. Thank you very much! Errors and omissions are mine. Please let me know about any errors you may spot. Thanks. - Henning

Links and References


(+)maintained at the time of writing, Feb 2011.


  • decrementing pool size could close sockets that are in use
  • spawn individual conn_mgr gen_server processes for each pool
  • allow row results to be returned as binary


Copyright (c) 2009-2011 Bill Warnecke, Jacob Vorreuter, Henning Diedrich, Eonblast Corporation

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.



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