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

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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 uses encoding-aware MySQL API calls where it can.

The API consists of three classes:

Mysql2::Client - your connection to the database.

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

Mysql2::Statement - returned from issuing a #prepare on the connection. Execute the statement to get a Result.


General Instructions

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 libmariadb-dev, 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.

Configuration options

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.

  • --with-openssl-dir[=/path/to/openssl] - Specify the directory where OpenSSL is installed. In most cases, the Ruby runtime and MySQL client libraries will link against a system-installed OpenSSL library and this option is not needed. Use this option when non-default library paths are needed.

  • --with-sanitize[=address,cfi,integer,memory,thread,undefined] - Enable sanitizers for Clang / GCC. If no argument is given, try to enable all sanitizers or fail if none are available. If a command-separated list of specific sanitizers is given, configure will fail unless they all are available. Note that the some sanitizers may incur a performance penalty, and the Address Sanitizer may require a runtime library. To see line numbers in backtraces, declare these environment variables (adjust the llvm-symbolizer path as needed for your system):

  export ASAN_SYMBOLIZER_PATH=/usr/bin/llvm-symbolizer-3.4
  export ASAN_OPTIONS=symbolize=1

Linux and other Unixes

You may need to install a package such as libmariadb-dev, libmysqlclient-dev, mysql-devel, or default-libmysqlclient-dev; 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 but is missing the header file mysql.h -- double check that you have the -dev packages installed.

Mac OS X

You may use Homebrew, MacPorts, 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.

If you have not done so already, you will need to install the XCode select tools by running xcode-select --install.

Later versions of MacOS no longer distribute a linkable OpenSSL library. It is common to use Homebrew or MacPorts to install OpenSSL. Make sure that both the Ruby runtime and MySQL client libraries are compiled with the same OpenSSL family, 1.0 or 1.1 or 3.0, since only one can be loaded at runtime.

$ brew install [email protected]
$ gem install mysql2 -- --with-openssl-dir=$(brew --prefix [email protected])


$ sudo port install openssl11

Since most Ruby projects use Bundler, you can set build options in the Bundler config rather than manually installing a global mysql2 gem. This example shows how to set build arguments with Bundler config:

$ bundle config --local build.mysql2 -- --with-openssl-dir=$(brew --prefix [email protected])

Another helpful trick is to use the same OpenSSL library that your Ruby was built with, if it was built with an alternate OpenSSL path. This example finds the argument --with-openssl-dir=/some/path from the Ruby build and adds that to the Bundler config:

$ bundle config --local build.mysql2 -- $(ruby -r rbconfig -e 'puts RbConfig::CONFIG["configure_args"]' | xargs -n1 | grep with-openssl-dir)

Note the additional double dashes (--) these separate command-line arguments that gem or bundler interpret from the addiitonal arguments that are passed to the mysql2 build process.


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 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
client = => "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"].is_a? Integer
  if row["dne"]  # non-existent hash entry is nil
    puts row["dne"]

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?

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

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

headers = results.fields # <= that's an array of field names, in order
types = results.field_types # <= that's an array of field types, 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"

Prepared statements are supported, as well. In a prepared statement, use a ? in place of each value and then execute the statement to retrieve a result set. Pass your arguments to the execute method in the same number and order as the question marks in the statement. Query options can be passed as keyword arguments to the execute method.

Be sure to read about the known limitations of prepared statements at

statement = @client.prepare("SELECT * FROM users WHERE login_count = ?")
result1 = statement.execute(1)
result2 = statement.execute(2)

statement = @client.prepare("SELECT * FROM users WHERE last_login >= ? AND location LIKE ?")
result = statement.execute(1, "CA")

statement = @client.prepare("SELECT * FROM users WHERE last_login >= ? AND location LIKE ?")
result = statement.execute(1, "CA", :as => :array)

Session Tracking information can be accessed with

c =
  host: "",
  username: "root",
  flags: "SESSION_TRACK",
  init_command: "SET @@SESSION.session_track_schema=ON"
c.query("INSERT INTO test VALUES (1)")
session_track_type = Mysql2::Client::SESSION_TRACK_SCHEMA
session_track_data = c.session_track(session_track_type)

The types of session track types can be found at

Connection options

You may set the following connection options in
  :socket = '/path/to/mysql.sock',
  :encoding = 'utf8',
  :read_timeout = seconds,
  :write_timeout = seconds,
  :connect_timeout = seconds,
  :connect_attrs = {:program_name => $PROGRAM_NAME, ...},
  :reconnect = true/false,
  :local_infile = true/false,
  :secure_auth = true/false,
  :default_file = '/path/to/my.cfg',
  :default_group = 'my.cfg section',
  :default_auth = 'authentication_windows_client'
  :init_command => sql

Connecting to MySQL on localhost and elsewhere

The underlying MySQL client library uses the :host parameter to determine the type of connection to make, with special interpretation you should be aware of:

  • An empty value or "localhost" will attempt a local connection:
    • On Unix, connect to the default local socket path. (To set a custom socket path, use the :socket parameter).
    • On Windows, connect using a shared-memory connection, if enabled, or TCP.
  • A value of "." on Windows specifies a named-pipe connection.
  • An IPv4 or IPv6 address will result in a TCP connection.
  • Any other value will be looked up as a hostname for a TCP connection.

SSL/TLS options

Setting any of the following options will enable an SSL/TLS 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.
  # ...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',
  :sslverify => true, # Removed in MySQL 8.0
  :ssl_mode => :disabled / :preferred / :required / :verify_ca / :verify_identity,

For MySQL versions 5.7.11 and higher, use :ssl_mode to prefer or require an SSL connection and certificate validation. For earlier versions of MySQL, use the :sslverify boolean. For details on each of the :ssl_mode options, see

The :ssl_mode option will also set the appropriate MariaDB connection flags:

:ssl_mode MariaDB option value

MariaDB does not support the :preferred or :verify_ca options. For more information about SSL/TLS in MariaDB, see and

Secure auth

Starting with 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

Flags option parsing

The :flags parameter accepts an integer, a string, or an array. The integer form allows the client to assemble flags from constants defined under Mysql2::Client such as Mysql2::Client::FOUND_ROWS. Use a bitwise | (OR) to specify several flags.

The string form will be split on whitespace and parsed as with the array form: Plain flags are added to the default flags, while flags prefixed with - (minus) are removed from the default flags.

Using Active Record's database.yml

Active Record typically reads its configuration from a file named database.yml or an environment variable DATABASE_URL. Use the value mysql2 as the adapter name. For example:

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

In this example, the compression flag is negated with -COMPRESS.

Using Active Record's DATABASE_URL

Active Record typically reads its configuration from a file named database.yml or an environment variable DATABASE_URL. Use the value mysql2 as the protocol name. For example:


Reading a MySQL config file

You may read configuration options from a MySQL configuration file by passing the :default_file and :default_group parameters. For example: => '/user/.my.cnf', :default_group => 'client')

Initial command on connect and reconnect

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. => "SET @@SESSION.sql_mode = 'STRICT_ALL_TABLES'")

Multiple result sets

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 = => "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

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


next_result: Unknown column 'A' in 'field list' (Mysql2::Error)

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 =
c.query_options.merge!(:symbolize_keys => true)


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


# this will set the options for the Mysql2::Result instance returned from the #execute method
c =
s = c.prepare(sql)
s.execute(arg1, args2, :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


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

Casting "boolean" columns

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

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

Keep in mind that this works only with fields and not with computed values, e.g. this result will contain 1, not true:

client =
result = client.query("SELECT true", :cast_booleans => true)

CAST function wouldn't help here as there's no way to cast to TINYINT(1). Apparently the only way to solve this is to use a stored procedure with return type set to TINYINT(1).

Skipping casting

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 =
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 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.

Row Caching

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:

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.

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 2.0 through 2.7 (all versions to date)
  • Ruby MRI 3.0, 3.1, 3.2 (all versions to date)
  • Rubinius 2.x and 3.x do work but may fail under some workloads

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

  • MySQL 5.5, 5.6, 5.7, 8.0
  • MySQL Connector/C 6.0, 6.1, 8.0 (primarily on Windows)
  • MariaDB 5.5, 10.x, with a focus on 10.6 LTS and 10.11 LTS
  • MariaDB Connector/C 2.x, 3.x

Ruby on Rails / Active Record

  • mysql2 0.5.x works with Rails / Active Record 4.2.11, 5.0.7, 5.1.6, and higher.
  • mysql2 0.4.x works with Rails / Active Record 4.2.5 - 5.0 and higher.
  • mysql2 0.3.x works with Rails / Active Record 3.1, 3.2, 4.x, 5.0.
  • mysql2 0.2.x works with Rails / Active Record 2.3 - 3.0.

Asynchronous Active Record

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

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

Benchmarks and Comparison

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

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 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.

Special Thanks

  • 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 - for TONS of help testing the Active Record adapter
  • Aaron Patterson - tons of contributions, suggestions and general badassness
  • Mike Perham - Async Active Record adapter (uses Fibers and EventMachine)
  • Aaron Stone - additional client settings, local files, microsecond time, maintenance support
  • Kouhei Ueno - for the original work on Prepared Statements way back in 2012
  • John Cant - polishing and updating Prepared Statements support
  • Justin Case - polishing and updating Prepared Statements support and getting it merged
  • Tamir Duberstein - for help with timeouts and all around updates and cleanups
  • Jun Aruga - for migrating CI tests to GitHub Actions and other improvements