Optimization Tips: Ruby on Rails and MySQL

Stop.

I’ve uncovered these tips after (at least) the 3rd refactoring effort of some fairly simple, straight-forward Rails code. Rails is great for getting ideas prototyped super fast. These tips will slow down development and make apps less portable. Continue reading only if you’re running a live app in production and not happy with how resource-intensive it is.

My approach to this round of optimization was watch the Load calculations in the development log and optimize transactions with a Load greater than 0.0009.

• First, a rule of thumb: Development boxes are faster than production boxes. If it’s acceptably fast locally, then it’ll probably be a turtle in production.
• Use Model.find_by_sql or Model.count_by_sql whenever possible.
  Slow: Person.find_by_name('JoeyJoeJoe')
  Fast: Person.find_by_sql("SELECT person.* WHERE person.name = 'JoeyJoeJoe'")
• Don’t put keys, IDs, or other numbers within quotes in your Finds
  Slow: WHERE id = "1234"
  Fast: WHERE id = 1234
• Only request the specific database column/model attribute you want
  Slow: Person.find_by_name('JoeyJoeJoe').height
  Fast: Person.find_by_sql("SELECT person.height WHERE person.name = 'JoeyJoeJoe'"). Put indexes on all these columns/attributes.
• Use connection.insert, connection.update, connection.delete for database transactions performed on an array of models or transactions that don’t need the overhead of a model.
• Slow: ...WHERE table_1.id = table_2.table1_id...
  Fast: ...table_1 JOIN table_2 ON table1.id = table_2.table1_id....
• Many tiny database transactions are faster than 1 big one
  Slow: stuff = Stuff.find_by_sql("SELECT everything.* FROM everything JOIN (box_1, box_2) ON (everything.id = box_1.everything_id box_2.box1_id = box_1.id")
  Fast: boxes = Boxes.find_by_sql("SELECT box_1.everything_id FROM box_1 JOIN box_2 ON box_2.box1_id = box_1.id")
  followed by
  boxes.each do |box_1|
stuff = Stuff.find_by_sql("SELECT everything.* FROM everything WHERE id = #{box_1.everything_id}
end
• If you’re running the InnoDB datastore (vs MyISAM) try cranking up your innodb_buffer_pool_size. I say start by doubling it. Seriously.
• Again, if you’re running InnoDB and doing a anything more involved than the simplest ORDER BY, try cranking up your sort_buffer_size and read_rnd_buffer_size to something in the double-digit M range.
• Also, if you’re comparing datastore engines, MyISAM has full text search, InnoDB doesn’t. So you’ll need a clever work around. There are a number of them.

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