Pgq

Queues system for AR/Rails based on PgQ Skytools for PostgreSQL, like Resque on Redis. Rails 2.3 and 3 compatible.

About PgQ

• http://wiki.postgresql.org/wiki/SkyTools#PgQ

Install

Install skytools: Ubuntu 11.10:

# apt-get install postgresql-server postgresql-client
# apt-get install skytools

Gemfile:

gem 'pgq'

Create ticker configs from database.yml:

$ rake pgq:generate_configs 
edit config: config/pgq_development.ini

Install pgq to database (if test database recreates all the time, should reinstall pgq each time):

$ rake pgq:install
or execute
$ pgqadm config/pgq_development.ini install

Run ticker daemon (ticker needs on production database, or development if we test the process of consuming): Daemon run once, bind to the database. (If worker not consuming check that daemon started).

$ rake pgq:ticker:start (stop)
or execute
$ pgqadm config/pgq_development.ini ticker -d

Last, add to config/application.rb

config.autoload_paths += %W( #{config.root}/app/workers )

Create Pgq consumer

$ rails generate pgq:add my

This creates file app/workers/pgq_my.rb and migration

$ rake db:migrate

class PgqMy < Pgq::Consumer

  def some_method1(a, b, c)
    logger.info "async call some_method1 with #{[a, b, c].inspect}"
  end
  
  def some_method2(x)
    logger.info "async called some_method2 with #{x.inspect}"
  end
  
end

Insert event into queue:

PgqMy.some_method1(1, 2, 3)

or
    
PgqMy.add_event(:some_method2, some_x)
        
or

PgqMy.enqueue(:some_method1, 1, 2, 3)

Workers

Start worker for queue:

$ rake pgq:worker QUEUES="my"
$ rake pgq:worker QUEUES="my,mailer,other"
$ rake pgq:worker QUEUES="all" RAILS_ENV=production

Also can consume manual, or write bin_script:

class PgqRunnerScript < BinScript

  self.enable_locking = false

  required :q, "queues separated by ','"
  required :w, "watch file"
  
  def do!
    worker = Pgq::Worker.new(:logger => self.logger, :queues => params(:q), 
                             :watch_file => params(:w) || "./tmp/stop_all.txt")
    worker.run
  end
                                                                     
end

and run:

$ ./bin/pgq_runner.rb -q my -l ./log/pgq_my.log
$ ./bin/pgq_runner.rb -q all -l ./log/pgq_all.log   # this will consume all queues from config/queues_list.yml

Admin interface

Realized by gem pgq_web.

Divide events between workers, for one consumer class

create more queues: my_2, my_3

class PgqMy < Pgq::Consumer

  QUEUES = %w(my my_2 my_3).freeze

  def self.next_queue_name
    QUEUES.choice
  end
  
end

And run 3 workers: for my, my_2, my_3

Consume group of events extracted from pgq(batch):

Usually batch size is ~500 events.

class PgqMy < Pgq::ConsumerGroup

  # {'type' => [events]}
  def perform_group(events_hash)
    raise "realize me"
  end
  
end

Options

create initializer with:

class Pgq::Consumer

  # specify database with pgq queues
  def self.database
    SomeDatabase 
  end

  # specify coder  
  def self.coder
    Marshal64 # class/module with self methods dump/load
  end
    
end

Proxy method to consumer

Usefull in specs

  PgqMy.proxy(:some_method1)

When code call PgqMy.some_method1(a,b,c) this would be convert into PgqMy.new.some_method1(a,b,c)

for Rails 2.3

Add to Rakefile:

load 'tasks/pgq.rake'

Copy generators from gem to lib/generators.

./script/generate pgq bla