auto-failover ReplicaSet config for MongoMapper, by way of ruby driver

gistfile1.txt

replica_sets = mm_env['replica_sets']  # node1:port&node2:port

rs_list = replica_sets.split("&").map {|rs| host,port = rs.split(":"); [host,port.to_i] }
    
MongoMapper.connection = Mongo::RetryReplicaSetConnection.new(*(rs_list << {:read_secondary => true, :auto_refresh  => true }))

MongoMapper.database = mm_env['database']
MongoMapper.database.authenticate(mm_env['username'], mm_env['password']) 

retry.rb

# encoding: utf-8

## pulled from mongoid

# Provides behaviour for retrying commands on connection failure.
module Mongo::Retry

  # Retries command on connection failures.
  #
  # This is useful when using replica sets. When a primary server wents
  # down and a command is issued, the driver will raise a
  # Mongo::ConnectionFailure. We wait a little bit, because nodes are
  # electing themselves, and then retry the given command.
  #
  # By setting Mongoid.max_retries_on_connection_failure to a value of 0,
  # no attempt will be made, immediately raising connection failure.
  # Otherwise it will attempt to make the specified number of retries
  # and then raising the exception to clients.
  #
  # @example Retry the command.
  #   retry_on_connection_failure do
  #     collection.send(name, *args)
  #   end
  #
  # @since 2.0.0
  def retry_on_connection_failure
    retries = 0
    begin
      yield
    rescue Mongo::ConnectionFailure => ex
      retries += 1
      raise ex if retries > 30  # Config.max_retries_on_connection_failure
      Kernel.sleep(0.5) ## Todo.. modify for event machine
      log_retry retries
      retry
    end
  end

  private

  def log_retry(retry_number)
    puts "A Mongo::ConnectionFailure was raised. Retry attempt ##{retry_number}."
  end
end

retry_replica_set_connetion.rb

class Mongo::RetryReplicaSetConnection < Mongo::ReplSetConnection
  ## wraps basic send message calls in catch blocks to auto retry connection
  
  
  ## per: http://permalink.gmane.org/gmane.comp.db.mongodb.user/25261
  
  # After looking at the Ruby MongoDB driver code it appears that we could
  # handle this transparently in the following methods:
  #   Connection::send_message
  #   Connection::send_message_with_safe_check
  #   Connection::receive_message

  # I put together a new Connection class that is derived from
  # ReplSetConnection to implement this behavior.
  
  ## This is ripped from Mongoid block 
  include Mongo::Retry
  
  
  
  def send_message(operation, message, opts={})
    retry_on_connection_failure do
      super(operation, message, opts)
    end
  end
  
  def send_message_with_safe_check(operation, message, db_name, log_message=nil, last_error_params=false)
    retry_on_connection_failure do
      super(operation, message, db_name, log_message, last_error_params)
    end
  end
  
  def receive_message(operation, message, log_message=nil, socket=nil, command=false)
    retry_on_connection_failure do
      super(operation, message, log_message, socket, command)
    end
  end
   
end

This works really well! Why is this not in mongomapper?

Given the nature of how it works, it's really not necessary to add it to mongomapper. That said, a slightly more integrated implementation would be useful, as not all database actions should be treated the same, which is the original argument for not including it in the ruby driver. However, I'm not really well versed enough with the internals of MM to make the addition.

…

-----Original Message----- From: Todd Troxell [mailto:reply@reply.github.com] Sent: Friday, October 07, 2011 10:04 PM To: bhbryant Subject: Re: gist gist: 1230938 This works really well! Why is this not in mongomapper? ## Reply to this email directly or view it on GitHub: https://gist.github.com/1230938

Makes sense! I think my main point is-- this must exist somewhere in the toolchain. Currently your gist ranks really high in Google because it is the only thing that works right now :)

@bhbryant aha even I got here.

Trying to make it work with latest mongo gem, rs_list is a different format now

If you could give me a hand modifying it to work that would be fantastic.

Getting a too many arguments error on the initialize

Thank you for this brilliant gist !

@thomasdavis, you should take a look at my fork I had to make.

Basically, it does not require you to change your connection adapter/class and fix the too many arguments error.

Good morning guys, I saw this and seems to work really well.
So my question is... is this gist already implemented into a gem or something like that?
If not, I'll apply as is here :)