Erlang Connection/Client Pool

ecpool is different with worker-pool libraries in that it is designed to pool connection/clients to server or database.

ecpool tries to avoid the erlang application crash when the server or database going down.

Overview

A pool worker to manage/monitor the connection to server or database:

PoolWorker -> Conn -> DB

Use client:

ecpool:with_client(Pool, fun(Client) -> call(Client) end).

Usage

Start the pool

ecpool:start_pool(Pool, Mod, Opts).

For example:

PgOpts = [%% Pool Size
          {pool_size, 10},
          %% Pool Type: round_robin | random | hash
          {pool_type, round_robin},
          %% Auto reconnect
          {auto_reconnect, 3},
          %% epgsql opts
          {host, "localhost"},
          {port, 5432},
          {username, "feng"},
          {password, ""},
          {database, "mqtt"},
          {encoding,  utf8}],
ecpool:start_pool(epgsql_pool, epgsql_pool_client, PgOpts)

The Callback Module

Pool Worker Callback:

-callback connect(ConnOpts :: list()) -> {ok, pid()} | {error, any()}.

For example, epgsql_pool_client module:

-module(epgsql_pool_client).
-behavihour(ecpool_worker).
connect(Opts) ->
    Host = proplists:get_value(host, Opts),
    Username = proplists:get_value(username, Opts),
    Password = proplists:get_value(password, Opts),
    epgsql:connect(Host, Username, Password, conn_opts(Opts)).
squery(Pool, Sql) ->
    ecpool:with_client(Pool, fun(Client) -> epgsql:squery(Client, Sql) end).

Design

The ecpool supervisor tree:

pool_sup[one_for_all supervisor]
    pool[gen-server]
    worker_sup[one_for_one supervisor]
        worker1 -> connection1
        worker2 -> connection1
        ....

Author

Feng Lee feng@emqx.io

License

The Apache License Version 2.0