We keep having the problem of delayed_job dying on us. So we decided to not let mysql #connect die on us.

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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 APIs 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 classes:

Mysql2::Client - your connection to the database.

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

gem install mysql2

This gem links against MySQL's libmysqlclient library or Connector/C library, and compatible alternatives such as MariaDB. You may need to install a package such as libmysqlclient-dev, mysql-devel, or other appropriate package for your system. See below for system-specific instructions.

By default, the mysql2 gem will try to find a copy of MySQL in this order:

• Option --with-mysql-dir, if provided (see below).
• Option --with-mysql-config, if provided (see below).
• Several typical paths for mysql_config (default for the majority of users).
• The directory /usr/local.

Use these options by gem install mysql2 -- [--optionA] [--optionB=argument].

• --with-mysql-dir[=/path/to/mysqldir] - Specify the directory where MySQL is installed. The mysql2 gem will not use mysql_config, but will instead look at mysqldir/lib and mysqldir/include for the library and header files. This option is mutually exclusive with --with-mysql-config.

• --with-mysql-config[=/path/to/mysql_config] - Specify a path to the mysql_config binary provided by your copy of MySQL. The mysql2 gem will ask this mysql_config binary about the compiler and linker arguments needed. This option is mutually exclusive with --with-mysql-dir.

• --with-mysql-rpath=/path/to/mysql/lib / --without-mysql-rpath - Override the runtime path used to find the MySQL libraries. This may be needed if you deploy to a system where these libraries are located somewhere different than on your build system. This overrides any rpath calculated by default or by the options above.

You may need to install a package such as libmysqlclient-dev or mysql-devel; refer to your distribution's package guide to find the particular package. The most common issue we see is a user who has the library file libmysqlclient.so but is missing the header file mysql.h -- double check that you have the -dev packages installed.

You may use MacPorts, Homebrew, or a native MySQL installer package. The most common paths will be automatically searched. If you want to select a specific MySQL directory, use the --with-mysql-dir or --with-mysql-config options above.

Make sure that you have Ruby and the DevKit compilers installed. We recommend the Ruby Installer distribution.

By default, the mysql2 gem will download and use MySQL Connector/C from mysql.com. If you prefer to use a local installation of Connector/C, add the flag --with-mysql-dir=c:/mysql-connector-c-x-y-z (this path may use forward slashes).

By default, the libmysql.dll library will be copied into the mysql2 gem directory. To prevent this, add the flag --no-vendor-libmysql. The mysql2 gem will search for libmysql.dll in the following paths, in order:

• Environment variable RUBY_MYSQL2_LIBMYSQL_DLL=C:\path\to\libmysql.dll (note the Windows-style backslashes).
• In the mysql2 gem's own directory vendor/libmysql.dll
• In the system's default library search paths.

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}'")

You can get a count of your results with results.count.

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
  puts row["id"] # row["id"].class == Fixnum
  if row["dne"]  # non-existant hash entry is nil
    puts row["dne"]
  end
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?

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

You can get the headers and the columns in the order that they were returned by the query like this:

headers = results.fields # <= that's an array of field names, in order
results.each(:as => :array) do |row|
# Each row is an array, ordered the same as the query results
# An otter's den is called a "holt" or "couch"
end

You may set the following connection options in Mysql2::Client.new(...):

Mysql2::Client.new(
  :host,
  :username,
  :password,
  :port,
  :database,
  :socket = '/path/to/mysql.sock',
  :flags = REMEMBER_OPTIONS | LONG_PASSWORD | LONG_FLAG | TRANSACTIONS | PROTOCOL_41 | SECURE_CONNECTION | MULTI_STATEMENTS,
  :encoding = 'utf8',
  :read_timeout = seconds,
  :write_timeout = seconds,
  :connect_timeout = seconds,
  :reconnect = true/false,
  :local_infile = true/false,
  :secure_auth = true/false,
  :default_file = '/path/to/my.cfg',
  :default_group = 'my.cfg section',
  :init_command => sql
  )

Setting any of the following options will enable an SSL connection, but only if your MySQL client library and server have been compiled with SSL support. MySQL client library defaults will be used for any parameters that are left out or set to nil. Relative paths are allowed, and may be required by managed hosting providers such as Heroku.

Mysql2::Client.new(
  # ...options as above...,
  :sslkey => '/path/to/client-key.pem',
  :sslcert => '/path/to/client-cert.pem',
  :sslca => '/path/to/ca-cert.pem',
  :sslcapath => '/path/to/cacerts',
  :sslcipher => 'DHE-RSA-AES256-SHA'
  )

You can also retrieve multiple result sets. For this to work you need to connect with flags Mysql2::Client::MULTI_STATEMENTS. Multiple result sets can be used with stored procedures that return more than one result set, and for bundling several SQL statements into a single call to client.query.

client = Mysql2::Client.new(:host => "localhost", :username => "root", :flags => Mysql2::Client::MULTI_STATEMENTS)
result = client.query('CALL sp_customer_list( 25, 10 )')
# result now contains the first result set
while client.next_result
  result = client.store_result
  # result now contains the next result set
end

Repeated calls to client.next_result will return true, false, or raise an exception if the respective query erred. When client.next_result returns true, call client.store_result to retrieve a result object. Exceptions are not raised until client.next_result is called to find the status of the respective query. Subsequent queries are not executed if an earlier query raised an exception. Subsequent calls to client.next_result will return false.

result = client.query('SELECT 1; SELECT 2; SELECT A; SELECT 3')
p result.first

while client.next_result
  result = client.store_result
  p result.first
end

Yields:

{"1"=>1}
{"2"=>2}
next_result: Unknown column 'A' in 'field list' (Mysql2::Error)

See https://gist.github.com/1367987 for using MULTI_STATEMENTS with Active Record.

Starting wih MySQL 5.6.5, secure_auth is enabled by default on servers (it was disabled by default prior to this). When secure_auth is enabled, the server will refuse a connection if the account password is stored in old pre-MySQL 4.1 format. The MySQL 5.6.5 client library may also refuse to attempt a connection if provided an older format password. To bypass this restriction in the client, pass the option :secure_auth => false to Mysql2::Client.new(). If using ActiveRecord, your database.yml might look something like this:

development:
  adapter: mysql2
  encoding: utf8
  database: my_db_name
  username: root
  password: my_password
  host: 127.0.0.1
  port: 3306
  secure_auth: false

You may read configuration options from a MySQL configuration file by passing the :default_file and :default_group paramters. For example:

Mysql2::Client.new(:default_file => '/user/.my.cnf', :default_group => 'client')

If you specify the init_command option, the SQL string you provide will be executed after the connection is established. If :reconnect is set to true, init_command will also be executed after a successful reconnect. It is useful if you want to provide session options which survive reconnection.

Mysql2::Client.new(:init_command => "SET @@SESSION.sql_mode = 'STRICT_ALL_TABLES'")

The default config hash is at:

Mysql2::Client.default_query_options

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)

or

# 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)

or

# 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)

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

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

Mysql2 now supports two timezone options:

:database_timezone # this is the timezone Mysql2 will assume fields are already stored as, and will use this when creating the initial Time objects in ruby
:application_timezone # this is the timezone Mysql2 will convert to before finally handing back to the caller

In other words, if :database_timezone is set to :utc - Mysql2 will create the Time objects using Time.utc(...) from the raw value libmysql hands over initially. Then, if :application_timezone is set to say - :local - Mysql2 will then convert the just-created UTC Time object to local time.

Both options only allow two values - :local or :utc - with the exception that :application_timezone can be [and defaults to] nil

You can now tell Mysql2 to cast tinyint(1) fields to boolean values in Ruby with the :cast_booleans option.

client = Mysql2::Client.new
result = client.query("SELECT * FROM table_with_boolean_field", :cast_booleans => true)

Mysql2 casting is fast, but not as fast as not casting data. In rare cases where typecasting is not needed, it will be faster to disable it by providing :cast => false. (Note that :cast => false overrides :cast_booleans => true.)

client = Mysql2::Client.new
result = client.query("SELECT * FROM table", :cast => false)

Here are the results from the query_without_mysql_casting.rb script in the benchmarks folder:

                           user     system      total        real
Mysql2 (cast: true)    0.340000   0.000000   0.340000 (  0.405018)
Mysql2 (cast: false)   0.160000   0.010000   0.170000 (  0.209937)
Mysql                  0.080000   0.000000   0.080000 (  0.129355)
do_mysql               0.520000   0.010000   0.530000 (  0.574619)

Although Mysql2 performs reasonably well at retrieving uncasted data, it (currently) is not as fast as the Mysql gem. In spite of this small disadvantage, Mysql2 still sports a friendlier interface and doesn't block the entire ruby process when querying.

NOTE: Not supported on Windows.

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.

By default, Mysql2 will cache rows that have been created in Ruby (since this happens lazily). This is especially helpful since it saves the cost of creating the row in Ruby if you were to iterate over the collection again.

If you only plan on using each row once, then it's much more efficient to disable this behavior by setting the :cache_rows option to false. This would be helpful if you wanted to iterate over the results in a streaming manner. Meaning the GC would cleanup rows you don't need anymore as you're iterating over the result set.

Mysql2::Client can optionally only fetch rows from the server on demand by setting :stream => true. This is handy when handling very large result sets which might not fit in memory on the client.

result = client.query("SELECT * FROM really_big_Table", :stream => true)

There are a few things that need to be kept in mind while using streaming:

• :cache_rows is ignored currently. (if you want to use :cache_rows you probably don't want to be using :stream)
• You must fetch all rows in the result set of your query before you can make new queries. (i.e. with Mysql2::Result#each)

Read more about the consequences of using mysql_use_result (what streaming is implemented with) here: http://dev.mysql.com/doc/refman/5.0/en/mysql-use-result.html.

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.

This caching behavior can be disabled by setting the :cache_rows option to false.

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

This gem is tested with the following Ruby versions on Linux and Mac OS X:

• Ruby MRI 1.8.7, 1.9.2, 1.9.3, 2.0.0, 2.1.x, 2.2.x (ongoing patch releases)
• Ruby Enterprise Edition (based on MRI 1.8.7)
• Rubinius 2.x

This gem is tested with the following MySQL and MariaDB versions:

• MySQL 5.0, 5.1, 5.5, 5.6, 5.7
• MySQL Connector/C 6.0 and 6.1 (primarily on Windows)
• MariaDB 5.5, 10.0

• mysql2 0.2.x includes an Active Record driver compatible with AR 2.3 and 3.0
• mysql2 0.3.x does not include an AR driver because it is included in AR 3.1 and above

Please see the em-synchrony project for details about using EventMachine with mysql2 and Rails.

Sequel includes a mysql2 adapter in all releases since 3.15 (2010-09-01). Use the prefix "mysql2://" in your connection specification.

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

The mysql2 gem converts MySQL field types to Ruby data types in C code, providing a serious speed benefit.

The do_mysql gem also converts MySQL fields types, but has a considerably more complex API and is still ~2x slower than mysql2.

The mysql gem returns only nil or string data types, leaving you to convert field values to Ruby types in Ruby-land, which is much slower than mysql2's C code.

For a comparative benchmark, the script below performs 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:

         user       system     total       real
Mysql2   0.750000   0.180000   0.930000   (1.821655)
do_mysql 1.650000   0.200000   1.850000   (2.811357)
Mysql    7.500000   0.210000   7.710000   (8.065871)

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

Use 'bundle install' to install the necessary development and testing gems:

bundle install
rake

The tests require the "test" database to exist, and expect to connect both as root and the running user, both with a blank password:

CREATE DATABASE test;
CREATE USER '<user>'@'localhost' IDENTIFIED BY '';
GRANT ALL PRIVILEGES ON test.* TO '<user>'@'localhost';

You can change these defaults in the spec/configuration.yml which is generated automatically when you run rake (or explicitly rake spec/configuration.yml).

For a normal installation on a Mac, you most likely do not need to do anything, though.

• Eric Wong - for the contribution (and the informative explanations) 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 Active Record adapter
• Aaron Patterson (http://github.com/tenderlove) - tons of contributions, suggestions and general badassness
• Mike Perham (http://github.com/mperham) - Async Active Record adapter (uses Fibers and EventMachine)
• Aaron Stone (http://github.com/sodabrew) - additional client settings, local files, microsecond time, maintenance support.