ActiveRecord Connection Pool

Active Record has ConnectionPool. A pool of TCP connections (not real database connections) for your web server.

[Web Server] <-> [ActiveRecord ConnectionPool] <-> [Database]

To configure Rails’s Connection Pool, change config/database.yml.

  pool: <%= Integer(ENV["RAILS_MAX_THREADS"] || 20) %>
  idle_timeout: 60

pool — How many number of connections Active Record can open with your database. If your database can only have 20 connections, and you have 4 servers. Then this value should be 5. Your Sidekiq workers also consume database connections.

idle_timeout — Number of seconds a connection will be kept unused in the pool before it automatically disconnected (default 300 seconds). The default is too long, it is better to change to 60.

AR::B = ActiveRecord::Base

To get a connection from Active Record, Model.connection.

When you finished using it, AR::B.clear_active_connections!.

You can also use AR::B.connection_pool.checkout to get a connection.

Return it by AR::B.connection_pool.checkin(connection).

Or use AR::B.connection_pool.with_connection(&block) with a block.