= 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.

== Installing

  gem install mysql2

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

== Usage

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
  end

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
  end

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
  end

== Async

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.

== ActiveRecord

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? :)

== EventMachine

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}"
    end

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

== 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.

== Compatibility

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.

== Benchmarks

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
  Mysql2
   0.890000   0.190000   1.080000 (  2.028887)
  Mysql
   7.330000   0.350000   7.680000 (  8.013160)
  do_mysql
   1.740000   0.220000   1.960000 (  2.909290)

== 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 (http://github.com/yury) - for TONS of help testing the ActiveRecord adapter