# ExRedisPool

A Elixir Redis client with connection pools.

## Features

ExRedisPool implements several features with a slightly different twist than
other Erlang/Elixir Redis clients.

## Dual Connection Pools

ExRedisPool supports two worker pools per process, one for synchronous queries
and another for asynchronous queries. The goal is to provide high quality of
service for calls that are waiting on a response, but also provide high
throughput when a response is not needed immediately.

By varying the size of the two work pools a relative throttle can be placed on the
asynchronous requests.

## Hostname Resolution on Startup

By default some Redis clients resolve the DNS name of your Redis host every time they
attempt to connect. In certain situations this DNS resolution can become a bottleneck
and it's better to resolve names into IP addresses when the work pools start up,
and only resolve them at that time.

An added benefit is that if you want to switch over to a new Redis host, you can control
the exact timing of the switch-over by restarting the ExRedisPool process.

## Installation

If [available in Hex](https://hex.pm/docs/publish), the package can be installed as:

  1. Add ex_redis_pool to your list of dependencies in `mix.exs`:

        def deps do
          [{:ex_redis_pool, "~> 0.0.1"}]
        end

  2. Ensure ex_redis_pool is started before your application:

        def application do
          [applications: [:ex_redis_pool]]
        end

## Usage

Start a new connection to the default Redis instance on localhost with a name:

```
iex(1)> pid = ExRedisPool.new(:redis_pool)
```

Or start a new connection to the default Redis instance on localhost without a name, just using the pid:

```
iex(2)> pid = ExRedisPool.new()
```

Either the pid or the atom name can be used to reference the connection.

### query

Using the pid from one of the new connections from above:

```
iex(3)> {:ok, "OK"} = ExRedisPool.q(pid, ["SET", "chuck", "norris"])
iex(4)> ExRedisPool.q(pid, ["GET", "chuck"])
"norris"
```

### query noreply

Using the pid from one of the new connections from above:

```
iex(5)> :ok = ExRedisPool.q_noreply(pid, ["SET", "chuck", "norris"])
iex(7)> :timer.sleep(100)
iex(8)> ExRedisPool.q(pid, ["GET", "chuck"])
"norris"
```

### query pipeline

Using the pid from one of the new connections from above:

```
iex(9)> [{:ok, "OK"}, {:ok, "OK"}] = ExRedisPool.qp(pid, [["SET", "chuck", "norris"], ["SET", "afraid", "nope"]])
iex(10)> ExRedisPool.q(pid, ["GET", "chuck"])
"norris"
iex(11)> ExRedisPool.q(pid, ["GET", "afraid"])
"nope"
```

### query pipeline noreply

Using the pid from one of the new connections from above:

```
iex(12)> :ok = ExRedisPool.qp_noreply(pid, [["SET", "chuck", "norris"], ["SET", "afraid", "nope"]])
iex(13)> :timer.sleep(100)
iex(14)> ExRedisPool.q(pid, ["GET", "chuck"])
"norris"
iex(15)> ExRedisPool.q(pid, ["GET", "afraid"])
"nope"
```

## TODO

- add read-only backup connections for fail-over