Demonstrate an issue with reaching the maxclients limit in Redis, even when using a connection pool.

README.md

Start a Redis server with a limited number of clients:

$> /usr/local/opt/redis/bin/redis-server --port 6380 --maxclients 5

Then, run the script:

$> ruby redis_connection_pool.rb

The script should fail with the following error during the second iteration:

ERR max number of clients reached (Redis::CommandError)

Run the script again with SHUTDOWN=true:

$> SHUTDOWN=true ruby redis_connection_pool.rb

This will allow the second iteration to complete successfully, since the connections from the first iteration will have been properly closed.

redis_connection_pool.rb

require 'redis'
require 'connection_pool'

2.times do
  pool = ConnectionPool.new(size: 5) { Redis.connect(port: 6380) } 

  pool.with { |connection| connection.set :count, 0 }

  5.times.collect {
    Thread.new do
      pool.with { |connection| connection.incr :count }
    end
  }.each(&:join)

  puts pool.with { |connection| connection.get :count }

  pool.shutdown { |connection| connection.quit } if ENV['SHUTDOWN']
end