Riak PBC Pool

Riak PBC Pool is a fork of [emysql] (https://github.com/eonblast/emysql "emysql") for the Riak protocol buffer client.

Overview

In the case of Emysql, each pool is given a unique identifier by the user. The Riak PBC pool functions differently in that it each pool consists of connections to one Riak server, so each pool can be referenced by using the Host and Port later.

Once a server has been added to the pool, a request to get a connection will be done in a round-robin fashion, instead of by specifying a pool to retrieve a connection from.

Important Note:

This code is not tested well; in fact, I just added code along with this README and comments update. Not sure if it all works. So, use at your own risk and I will up the version after I've tested/fixed. Whatever bugs you find, I would be glad to fix.

Connection locking

The Emysql application has a mechanism for locking. Once a connection has been retrieved from the pool, it locks the connection by making it unavailable when retrieving a new connection. To make the connection available, it must be put back in the pool manually.

Usage

Starting

To start the pool, issue the command:

riakpool:start()

This will start crypto, then start the riakpool application. If you have configured connections in the .app or the application .config file, it will create pools for each server listed in the conns list. The first entry in the tuple is the host, the second is the port, third is the number of connections to open and the final item in the tuple is a list of options to pass to riakc_pb_socket:start_link().

Adding pools

To add a new pool, call the function riakpool:add_pool(host(), port()). You can also specify the size and options. Example:

riakpool:add_pool("127.0.0.1", 8087, 5, [{auto_reconnect, false}]).

Removing pools

If you would like to remove a pool, you can remove it by calling riakpool:remove_pool(host(), port()).

riakpool:remove_pool("127.0.0.1", 8087).

Adding connections to pools

Because each pool is one server configuration, if we want to add more connections to that pool, we cannot simply add another named pool with the same connection information. So, we can increment the number of connections contained in one pool.

riakpool:increment_pool_size("127.0.0.1", 8087, 5).

This will increment the pool for host="127.0.0.1" and port=8087 by five connections.

Removing connections from pools

It is also possible to remove connections from the pool:

riakpool:decrement_pool_size("127.0.0.1", 8087, 2).

This will remove two connections.

Getting a connection

Currently, it is slightly inconvenient to get a connection. To get a connection, call riakpool:get_conn(). This will return a connection record, which has the Riak connection pid. Example:

Conn = riakpool:get_conn(),
{ok, Obj} = riakc_pb_socket:get(Conn#connection.pid, <<"bucket">>, <<"key">>).

This is, however, pretty crappy because a record is returned, and not just the Pid. Look for this to change in the future.

Returning a connection

Because we lock any connection that is being used, it's very important to return the connections back to the pool, or face getting errors because there are no available connections. To return a connection to the pool:

riakpool:return_conn(Connection).

TODO:

(In no particular order)

• Make riakpool:get_conn() return only the Pid
• Use Lager for logging statements
• ??
• Profit!