Episode #494 – September 9th, 2014

This episode covers RSpec 3.1, unifying multiple analytics services with Rack::Tracker, new features in Rails 4.2, the Fearless Rails Deployment book, a spike for thoughts about Rack 2.0 with The_Metal and RubyConf Portugal.

Forklift: Moving Big Databases Around

April 12, 2013

What?

Forklift is a ruby gem that can help you collect, augment, and save copies of your mySQL databases. This is often called an “ETL” tool as the steps in this process mirror the actions of “Extracting the data,” “Transforming the data,” and finally “Loading the data” into its final place.

With Forklift, you create a Plan which describes how to manipulate your data. The process for this involves (at least) three databases:

Live Set
Working Database
Final Database

The “Live Set” is first loaded into the “Working Set” to create a copy of your production data we can manipulate without fear of breaking replication. Then, any transformations/manipulations are run on the data in the working set. This might include normalizing or cleaning up data which was great for production but hard for analysts to use. Finally, when all of your transformations are complete, that data is loaded into the final database.

Forklift is appropriate to use by itself or integrated within a larger project. Forklift aims to be as fast as can be by using native mySQL copy commands and eschewing all ORMs and other RAM hogs.

Features

Can extract data from both local and remote databases
Can perform integrity checks on your source data to determine if this run of Forklift should be executed
Can run each Extract either each run or at a frequency
Can run each Transform either each run or at a frequency
Data kept in the woking database after each run to be used on subsequent transformations
Only ETL’d tables will be copied into the final database, leaving other tables untouched
Emails sent on errors

What does TaskRabbit use this for?

At TaskRabbit, the website you see at www.taskrabbit.com is actually made up of many smaller rails applications. When analyzing our site, we need to collect all of this data into one place so we can easily join across it.

We replicate all of our databases into one server in our office, and then use Forklift to extract the data we want into a common place. This gives us the option to both look at live data and to have a more accessible transformed set which we create on a rolling basis. Our “Forklift Loop” also git-pulls to check for any new transformations before each run.

Example Annotated Plan

In Forklift, you build a plan. You can add any action to the plan in any order before you run it. You can have 0 or many actions of each type.

require 'rubygems'
require 'bundler'
Bundler.require(:default)
require 'forklift/forklift' # Be sure to have installed the gem!

#########
# SETUP #
#########

forklift = Forklift::Plan.new({
  
  :local_connection => {
    :host => "localhost",
    :username => "root",
    :password => nil,
  },
  
  :remote_connections => [
    {
      :name => "remote_connection_a",
      :host => "192.168.0.0",
      :username => "XXX",
      :password => "XXX",
    },
    {
      :name => "remote_connection_b",
      :host => "192.168.0.1",
      :username => "XXX",
      :password => "XXX",
    },
  ],

  :final_database => "FINAL",
  :working_database => "WORKING",

  :do_dump? => true,
  :dump_file => "/data/backups/dump-#{Time.new}.sql.gz",

  :do_email? => true,
  :email_to => ['XXX'],
  :email_options => { 
    :via => :smtp, 
    :via_options => {
      :address              => 'smtp.gmail.com',
      :port                 => '587',
      :enable_starttls_auto => true,
      :user_name            => "XXX",
      :password             => "XXX",
      :authentication       => :plain,
    } 
  }

})

##########
# CHECKS #
##########

forklift.check_local_source({
  :name => 'CHECK_FOR_NEW_DATA',
  :database => 'test',
  :query => 'select (select max(created_at) from new_table) > (select date_sub(NOW(), interval 1 day))',
  :expected => '1'
})

forklift.check_remote_source({
  :connection_name => "remote_connection_b",
  :name => 'ANOTHER_CHECK',
  :database => 'stuff',
  :query => 'select count(1) from people',
  :expected => '100'
})

###########
# EXTRACT #
###########

forklift.import_local_database({
  :database => "database_1",
  :prefix => false,
  :frequency => 24 * 60 * 60,
})

forklift.import_local_database({
  :database => "database_2",
  :prefix => false,
  :only => ['table_1', 'table_2'],
})

forklift.import_remote_database({
  :connection_name => 'remote_connection_a',
  :database => "database_3",
  :prefix => true,
  :skip => ['schema_migrations']
})

#############
# TRANSFORM #
#############

transformation_base = File.dirname(__FILE__) + "/transformations"

forklift.transform_sql({
  :file => "#{transformation_base}/calendars/create_calendars.sql",
  :frequency => 24 * 60 * 60,
})

forklift.transform_ruby({
  :file => "#{transformation_base}/test/test.rb",
})

#######
# RUN #
#######

forklift.run

Workflow

def run
  lock_pidfile                # Ensure that only one instance of Forklift is running
  rebuild_working_database    # Ensure that the working database exists
  ensure_forklift_data_table  # Ensure that the metadata table for forklift exists (used for frequency calculations)
  
  run_checks                  # Preform any data integrity checks
  run_extractions             # Extact data from the life databases into the working database
  run_transformations         # Perform any transformations
  run_load                    # Load the manipulated data into the final database
  
  save_dump                   # mySQLdump the new final database for safe keeping
  send_email                  # Email folks the status of this forklift
  unlock_pidfile              # Clean up the pidfile so I can run next time
end

Transformations

Forklift allows you to create both Ruby transformations and SQL transformations

Ruby Transformations

SQL Transformations are kept in a file ending in .rb
Ruby Transformations should define a class which matches the name of the file (IE: class MyTransformation would be in a file called my_transformation.rb
logger.log(message) is the best way to log but logger.debug is also available
database is a string containing the name of the working database
connection is an instance of Forklift::Connection and connection.connection is a raw mysql2 connection
Classes need to define a transform(connection, database, logger) IE:

class Test

  def transform(connection, database, logger)
    logger.log "Running on DB: #{database}"
    logger.log "Counting users..."
    connection.q("USE `#{database}`")
    users_count = connection.q("count(1) as 'users_count' from `users`")
    logger.log("There were #{users_count} users")
  end

end

SQL Transformations

SQL Transformations are kept in a file ending in .sql
You can have many SQL statements per file
SQL will be executed linearly as it is written in the file

SQL Transformations can be used to generate new tables like this as well

Defaults

The defaults for a new Forklift::Plan are:

{
   :project_root => Dir.pwd,
   :lock_with_pid? => true,

   :final_database => {},
   :local_database => {},
   :forklift_data_table => '_forklift',
   
   :verbose? => true,

   :do_checks? => true,
   :do_extract? => true,
   :do_transform? => true,
   :do_load? => true,
   :do_email? => false,
   :do_dump? => false,
 }

Methods

Test

forklift.check_local_source({
  :name => STRING,     # A name for the test
  :database => STRING, # The Database to test
  :query => STRING,    # The Query to Run.  Needs to return only 1 row with 1 value
  :expected => STRING  # The response to compare against
})

forklift.check_remote_source({
  :connection_name => STRING,  # The name of the remote_connection
  :name => STRING,             # A name for the test
  :database => STRING,         # The Database to test
  :query => STRING,            # The Query to Run.  Needs to return only 1 row with 1 value
  :expected => STRING          # The response to compare against
})

Extract

forklift.import_local_database({
  :database => STRING,              # The Database to Extract
  :prefix => BOOLEAN,               # Should we prefix the names of all tables in this database when imported wight the database?
  :frequency => INTEGER (seconds),  # How often should we import this database?
  :skip => ARRAY OR STRINGS          # A list of tables to ignore and not import
  :only => ARRAY OR STRINGS          # A list of tables to ignore and not import (use :only or :skip, not both)
})

forklift.import_remote_database({
  :connection_name => STRING,       # The name of the remote_connection
  :database => STRING,              # The Database to Extract
  :prefix => BOOLEAN,               # Should we prefix the names of all tables in this database when imported wight the database?
  :frequency => INTEGER (seconds),  # How often should we import this database?
  :skip => ARRAY OR STRINGS          # A list of tables to ignore and not import
  :only => ARRAY OR STRINGS          # A list of tables to ignore and not import (use :only or :skip, not both)
})

Transform

forklift.transform_sql({
  :file => STRING,                 # The transformation file to run
  :frequency => INTEGER (seconds), # How often should we run this transformation?
})

forklift.transform_ruby({
  :file => STRING,                 # The transformation file to run
  :frequency => INTEGER (seconds), # How often should we run this transformation?
})

Debug

You can launch forklift in “debug mode” with --debug (we check ARGV["--debug"] and ARGV["-debug"]). In debug mode the following will happen: - verbose = true - no SQL will be run (extract, load) - no transforms will be run - no email will be sent - no mySQL dumps will be created

Options & Notes

email_options is a hash consumed by the Pony mail gem
Forklift’s logger is Lumberjack with a wrapper to also echo the log lines to stdout and save them to an array to be accessed later by the email system.
The connections hash will be passed directly to a mysql2 connection. Follow the link to see all the available options.

Limitations

mySQL only (the mysql2 gem specifically)

Forklift is available now. Enjoy!

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