connection_pool
Generic connection pooling for Ruby.
MongoDB has its own connection pool. ActiveRecord has its own connection pool.
This is a generic connection pool that can be used with anything, e.g. Redis,
Dalli and other Ruby network clients.
Usage
Create a pool of objects to share amongst the fibers or threads in your Ruby
application:
$memcached = ConnectionPool.new(size: 5, timeout: 5) { Dalli::Client.new }
Then use the pool in your application:
$memcached.with do, conn, conn.get('some-count')
end
If all the objects in the connection pool are in use, with will block
until one becomes available. If no object is available within :timeout seconds,
with will raise a Timeout::Error.
Optionally, you can specify a timeout override using the with-block semantics:
$memcached.with(timeout: 2.0) do, conn, conn.get('some-count')
end
This will only modify the resource-get timeout for this particular
invocation. This is useful if you want to fail-fast on certain non critical
sections when a resource is not available, or conversely if you are comfortable
blocking longer on a particular resource. This is not implemented in the below
ConnectionPool::Wrapper class.
Migrating to a Connection Pool
You can use ConnectionPool::Wrapper to wrap a single global connection,
making it easier to migrate existing connection code over time:
$redis = ConnectionPool::Wrapper.new(size: 5, timeout: 3) { Redis.connect }
$redis.sadd('foo', 1)
$redis.smembers('foo')
The wrapper uses method_missing to checkout a connection, run the requested
method and then immediately check the connection back into the pool. It's
not high-performance so you'll want to port your performance sensitive code
to use with as soon as possible.
$redis.with do, conn, conn.sadd('foo', 1)
conn.smembers('foo')
end
Once you've ported your entire system to use with, you can simply remove
Wrapper and use the simpler and faster ConnectionPool.
Shutdown
You can shut down a ConnectionPool instance once it should no longer be used.
Further checkout attempts will immediately raise an error but existing checkouts
will work.
cp = ConnectionPool.new { Redis.new }
cp.shutdown {, conn, conn.quit }
Shutting down a connection pool will block until all connections are checked in and closed.
Note that shutting down is completely optional; Ruby's garbage collector will reclaim
unreferenced pools under normal circumstances.
Current State
There are several methods that return information about a pool.
cp = ConnectionPool.new(size: 10) { Redis.new }
cp.size # => 10
cp.available # => 10
cp.with do, conn, cp.size # => 10
cp.available # => 9
end
Notes
- Connections are lazily created as needed.
- There is no provision for repairing or checking the health of a connection;
connections should be self-repairing. This is true of the Dalli and Redis
clients. - WARNING: Don't ever use
Timeout.timeoutin your Ruby code or you will see
occasional silent corruption and mysterious errors. The Timeout API is unsafe
and cannot be used correctly, ever. Use proper socket timeout options as
exposed by Net::HTTP, Redis, Dalli, etc.
Author
Mike Perham, @mperham, http://mikeperham.com