ActiveRecord host pooling

This gem allows for one ActiveRecord connection to be used to connect to multiple databases on a server. It accomplishes this by calling select_db() as necessary to switch databases between database calls.

How Connections Are Pooled

ARHP creates separate connection pools based on the pool key.

The pool key is defined as:

host / port / socket / username / replica

Therefore two databases with identical host, port, socket, username, and replica status will share a connection pool. If any part (host, port, etc.) of the pool key differ, two databases will not share a connection pool.

replica in the pool key is a boolean indicating if the database is a replica/reader (true) or writer database (false).

Below, test_pool_1 and test_pool_2 have identical host, username, socket, and replica status but the port information differs. Here the database configurations are formatted as a table to give a visual example:

	test_pool_1	test_pool_2
host	127.0.0.1	127.0.0.1
port		3306
socket
username	root	root
replica	false	false

The configuration items must be explicitly defined or they will be blank in the pool key. Configurations with matching implicit items but differing explicit items will create separate pools. e.g. test_pool_1 will default to port 3306 but because it is not explicitly defined it will not share a pool with test_pool_2

ARHP will therefore create the following pool keys:

test_pool_1 => 127.0.0.1///root/false
test_pool_2 => 127.0.0.1/3306//root/false

Support

For now, the only backend known to work is MySQL, with the mysql2 or activerecord-trilogy-adapter gem. When using the activerecord-trilogy-adapter ensure that the transitive dependency Trilogy is v2.5.0+. Postgres, from an informal reading of the docs, will never support the concept of one server connection sharing multiple dbs.

Installation

$ gem install active_record_host_pool

and make sure to require 'active_record_host_pool' in some way.

Testing

You need a local user called 'john-doe'.

mysql -uroot
CREATE USER 'john-doe'@'localhost';
GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP,INDEX  ON *.* TO 'john-doe'@'localhost';
FLUSH PRIVILEGES;

With mysql running locally, run

BUNDLE_GEMFILE=gemfiles/rails6.1.gemfile bundle exec rake test

Or

BUNDLE_GEMFILE=gemfiles/rails6.1.gemfile ruby test/test_arhp.rb --seed 19911 --verbose

Copyright

Copyright (c) 2011 Zendesk. See MIT-LICENSE for details.

Authors

Ben Osheroff [email protected], Mick Staugaard [email protected]