A modern, simple and very fast Mysql library for Ruby - binding to libmysql
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Mysql2 - A modern, simple and very fast Mysql library for Ruby - binding to libmysql

The Mysql2 gem is meant to serve the extremely common use-case of connecting, querying and iterating on results. Some database libraries out there serve as direct 1:1 mappings of the already complex C API's available. This one is not.

It also forces the use of UTF-8 [or binary] for the connection [and all strings in 1.9, unless Encoding.default_internal is set then it'll convert from UTF-8 to that encoding] and uses encoding-aware MySQL API calls where it can.

The API consists of two clases:

Mysql2::Client - your connection to the database

Mysql2::Result - returned from issuing a #query on the connection. It includes Enumerable.


gem install mysql2

You may have to specify –with-mysql-config=/some/random/path/bin/mysql_config


Connect to a database:

# this takes a hash of options, almost all of which map directly
# to the familiar database.yml in rails
# See http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/MysqlAdapter.html
client = Mysql2::Client.new(:host => "localhost", :username => "root")

Then query it:

results = client.query("SELECT * FROM users WHERE group='githubbers'")

Need to escape something first?

escaped = client.escape("gi'thu\"bbe\0r's")
results = client.query("SELECT * FROM users WHERE group='#{escaped}'")

Finally, iterate over the results:

results.each do |row|
  # conveniently, row is a hash
  # the keys are the fields, as you'd expect
  # the values are pre-built ruby primitives mapped from their corresponding field types in MySQL
  # Here's an otter: http://farm1.static.flickr.com/130/398077070_b8795d0ef3_b.jpg

Or, you might just keep it simple:

client.query("SELECT * FROM users WHERE group='githubbers'").each do |row|
  # do something with row, it's ready to rock

How about with symbolized keys?

# NOTE: the :symbolize_keys and future options will likely move to the #query method soon
client.query("SELECT * FROM users WHERE group='githubbers'").each(:symbolize_keys => true) do |row|
  # do something with row, it's ready to rock

Cascading config

The default config hash is at:


which defaults to:

{:async => false, :as => :hash, :symbolize_keys => false}

that can be used as so:

# these are the defaults all Mysql2::Client instances inherit
Mysql2::Client.default_query_options.merge!(:as => :array)


# this will change the defaults for all future results returned by the #query method _for this connection only_
c = Mysql2::Client.new
c.query_options.merge!(:symbolize_keys => true)


# this will set the options for the Mysql2::Result instance returned from the #query method
c = Mysql2::Client.new
c.query(sql, :symbolize_keys => true)

Result types

Array of Arrays

Pass the {:as => :array} option to any of the above methods of configuration

Array of Hashes

The default result type is set to :hash, but you can override a previous setting to something else with {:as => :hash}


I may add support for {:as => :csv} or even {:as => :json} to allow for much more efficient generation of those data types from result sets. If you'd like to see either of these (or others), open an issue and start bugging me about it ;)


You can set the :timezone option to :local or :utc to tell Mysql2 which timezone you'd like to have Time objects in


Mysql2::Client takes advantage of the MySQL C API's (undocumented) non-blocking function mysql_send_query for all queries. But, in order to take full advantage of it in your Ruby code, you can do:

client.query("SELECT sleep(5)", :async => true)

Which will return nil immediately. At this point you'll probably want to use some socket monitoring mechanism like EventMachine or even IO.select. Once the socket becomes readable, you can do:

# result will be a Mysql2::Result instance
result = client.async_result

NOTE: Because of the way MySQL's query API works, this method will block until the result is ready. So if you really need things to stay async, it's best to just monitor the socket with something like EventMachine. If you need multiple query concurrency take a look at using a connection pool.


To use the ActiveRecord driver, all you should need to do is have this gem installed and set the adapter in your database.yml to “mysql2”. That was easy right? :)

Asynchronous ActiveRecord

You can also use Mysql2 with asynchronous Rails (first introduced at www.mikeperham.com/2010/04/03/introducing-phat-an-asynchronous-rails-app/) by setting the adapter in your database.yml to “em_mysql2”. You must be running Ruby 1.9, thin and the rack-fiber_pool middleware for it to work.


The mysql2 EventMachine deferrable api allows you to make async queries using EventMachine, while specifying callbacks for success for failure. Here's a simple example:

require 'mysql2/em'

EM.run do
  client1 = Mysql2::EM::Client.new
  defer1 = client1.query "SELECT sleep(3) as first_query"
  defer1.callback do |result|
    puts "Result: #{result.to_a.inspect}"

  client2 = Mysql2::EM::Client.new
  defer2 = client2.query "SELECT sleep(1) second_query"
  defer2.callback do |result|
    puts "Result: #{result.to_a.inspect}"

Lazy Everything

Well… almost ;)

Field name strings/symbols are shared across all the rows so only one object is ever created to represent the field name for an entire dataset.

Rows themselves are lazily created in ruby-land when an attempt to yield it is made via #each. For example, if you were to yield 4 rows from a 100 row dataset, only 4 hashes will be created. The rest will sit and wait in C-land until you want them (or when the GC goes to cleanup your Mysql2::Result instance). Now say you were to iterate over that same collection again, this time yielding 15 rows - the 4 previous rows that had already been turned into ruby hashes would be pulled from an internal cache, then 11 more would be created and stored in that cache. Once the entire dataset has been converted into ruby objects, Mysql2::Result will free the Mysql C result object as it's no longer needed.

As for field values themselves, I'm workin on it - but expect that soon.


The specs pass on my system (SL 10.6.3, x86_64) in these rubies:

  • 1.8.7-p249

  • ree-1.8.7-2010.01

  • 1.9.1-p378

  • ruby-trunk

  • rbx-head - broken at the moment, working with the rbx team for a solution

The ActiveRecord driver should work on 2.3.5 and 3.0

Yeah… but why?

Someone: Dude, the Mysql gem works fiiiiiine.

Me: It sure does, but it only hands you nil and strings for field values. Leaving you to convert them into proper Ruby types in Ruby-land - which is slow as balls.

Someone: OK fine, but do_mysql can already give me back values with Ruby objects mapped to MySQL types.

Me: Yep, but it's API is considerably more complex and can be ~2x slower.


Performing a basic “SELECT * FROM” query on a table with 30k rows and fields of nearly every Ruby-representable data type, then iterating over every row using an #each like method yielding a block:

# These results are from the query_with_mysql_casting.rb script in the benchmarks folder

 user       system     total       real
 0.750000   0.180000   0.930000 (  1.821655)
 1.650000   0.200000   1.850000 (  2.811357)
 7.500000   0.210000   7.710000 (  8.065871)

Special Thanks

  • Eric Wong - for the contribution (and informative explanations of) of some thread-safety, non-blocking I/O and cleanup patches. You rock dude

  • Yury Korolev (github.com/yury) - for TONS of help testing the ActiveRecord adapter

  • Aaron Patterson (github.com/tenderlove) - tons of contributions, suggestions and general badassness

  • Mike Perham (github.com/mperham) - Async ActiveRecord adapter (uses Fibers and EventMachine)