MySQL/OTP + hnc

MySQL/OTP + hnc provides connection pooling for MySQL/OTP using hnc. It contains convenience functions for executing SQL queries on a connection in a pool and lets you choose between two methods for creating and managing connection pools:

Use it as a library that helps you supervise your own MySQL connection pools.
Use it as an application that manages its own supervisor for connection pools.

I want to supervise my own connection pools

Use mysql_hnc:child_spec/3 to get a child spec for a pool that you can use in your own supervisor.

%% my own supervisor
init([]) ->
    PoolOptions  = #{size => {5, 10}},
    MySqlOptions = [{user, "aladdin"}, {password, "sesame"}, {database, "test"},
                    {prepare, [{foo, "SELECT * FROM foo WHERE id=?"}]}],
    ChildSpecs = [
        %% MySQL pools
        mysql_hnc:child_spec(pool1, PoolOptions, MySqlOptions),
        %% other workers...
        {some_other_worker, {some_other_worker, start_link, []},
         permanent, 10, worker, [some_other_worker]}
    ],
    {ok, #{strategy => one_for_one}, ChildSpecs}}.

Let MySQL/OTP + hnc supervise my pools

This approach requires you to start the application mysql_hnc. Typically this is done by adding {applications, [mysql_hnc]} to your .app.src file and then relying on your favourite release tool for the rest.

Pools can be added at run-time using mysql_hnc:add_pool/3.

Pools can also be created at start-up by defining configuration parameters for mysql_hnc. The name of each configuration parameter is the pool name and the value is a pair on the form {PoolOptions, MySqlOptions}.

Example:

Start your Erlang node with erl -config mypools.config where mypools.config is a file with the following contents:

[
 {mysql_hnc, [
    {pool1, {#{size => {5, 10}},
             [{user, "aladdin"}, {password, "sesame"}, {database, "test"},
              {prepare, [{foo, "SELECT * FROM foo WHERE id=?"}]}]}}
]}].

Using the connection pools

The most commonly used MySQL functions are available with wrappers in mysql_hnc.

1> mysql_hnc:query(pool1, "SELECT * FROM foo WHERE id=?", [42]).
{ok,[<<"id">>,<<"bar">>],[[42,<<"baz">>]]}
2> mysql_hnc:execute(pool1, foo, [42]).
{ok,[<<"id">>,<<"bar">>],[[42,<<"baz">>]]}

For transactions, the connection pid is passed to the transaction fun as the first parameter.

3> mysql_hnc:transaction(pool1, fun (Pid) ->
       ok = mysql:query(Pid, "INSERT INTO foo VALUES (?, ?)", [1, <<"banana">>]),
       ok = mysql:query(Pid, "INSERT INTO foo VALUES (?, ?)", [2, <<"kiwi">>]),
       hello
   end).
{atomic, hello}

Sometimes you need to checkout a connection to execute multiple queries on it, without wrapping it in an SQL transaction. For this purpose you can use either a pair of calls to checkout/1 and checkin/1 or a call to with/2 with a fun as in this example:

4> mysql_hnc:with(pool1, fun (Pid) ->
       {ok, _, [[OldTz]]} = mysql:query(Pid, "SELECT @@time_zone"),
       ok = mysql:query(Pid, "SET time_zone = '+00:00'"),
       %% Do some stuff in the UTC time zone...
       ok = mysql:query(Pid, "SET time_zone = ?", [OldTz])
   end).
ok

Using `checkout/1` and `checkin/1`

The function checkout/1 does not return a MySQL connection directly but a connection identifier (actually, a hnc worker identifier). You have to unpack the real connection with a call to get_connection/1 first.

Accordingly, the function checkin/1 does not expect a MySQL connection but the connection identifier from which it was unpacked.

Use this as a dependency

Using erlang.mk, put this in your Makefile:

DEPS = mysql_hnc
dep_mysql_hnc = git https://github.com/mysql-otp/mysql-otp-hnc 0.2.0

Using rebar, put this in your rebar.config:

{deps, [
    {mysql_hnc, ".*", {git, "https://github.com/mysql-otp/mysql-otp-hnc",
                           {tag, "0.2.0"}}}
]}.

License

GNU Lesser General Public License (LGPL) version 3 or any later version. Since the LGPL is a set of additional permissions on top of the GPL, both license texts are included in the files COPYING.LESSER and COPYING respectively.

juhlig/mysql-otp-hnc