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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.

Installing

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:

Configuration options

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

  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 libmysqlclient.so but is missing the header file mysql.h -- double check that you have the -dev packages installed.

macOS

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, 3.x, since only one can be loaded at runtime.

$ brew install openssl@3 zstd
$ gem install mysql2 -- --with-openssl-dir=$(brew --prefix openssl@3)

or

$ sudo port install openssl3

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 openssl@3)

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 additional arguments that are passed to the mysql2 build process.

Windows

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

By default, the precompiled mysql2 gem for Windows vendors MariaDB Connector/C, built from the same MSYS2 mingw-w64 package a native Windows build installs via pacman (see the gemspec's msys2_mingw_dependencies). If you prefer to use a local installation of Connector/C, add the flag --with-mysql-dir=c:/path/to/connector-c (this path may use forward slashes).

By default, the libmariadb.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 libmariadb.dll in the following paths, in order:

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 https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/Mysql2Adapter.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"].is_a? Integer
  if row["dne"]  # non-existent 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).each do |row|
  # do something with row, it's ready to rock
end

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"
end

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 https://dev.mysql.com/doc/c-api/9.7/en/c-api-prepared-statement-problems.html

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 = {Mysql2::Client.new}(
  host: "127.0.0.1",
  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 https://dev.mysql.com/doc/refman/5.7/en/session-state-tracking.html

Connection options

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 | ..., # not exhaustive, see "Flags option parsing" below
  :encoding = 'utf8mb4',
  :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,
  :get_server_public_key = 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:

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.

{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',
  :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 https://dev.mysql.com/doc/refman/8.0/en/connection-options.html.

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

:ssl_mode MariaDB option value
:disabled MYSQL_OPT_SSL_ENFORCE = 0
:required MYSQL_OPT_SSL_ENFORCE = 1
:verify_ca MYSQL_OPT_SSL_VERIFY_SERVER_CERT = 1
:verify_identity MYSQL_OPT_SSL_VERIFY_SERVER_CERT = 1

MariaDB Connector/C has no CA-only verification mode, so :verify_ca gets the same full verification (CA and hostname) that :verify_identity gets -- MYSQL_OPT_SSL_VERIFY_SERVER_CERT is the only verification it offers. MariaDB does not support the :preferred option; there's no equivalent to fall back to. For more information about SSL/TLS in MariaDB, see https://mariadb.com/kb/en/securing-connections-for-client-and-server/ and https://mariadb.com/kb/en/mysql_optionsv/#tls-options

To set the TLS Server Name Indication (SNI) hostname sent during the TLS handshake, e.g. when connecting through a proxy that routes by hostname:

{Mysql2::Client.new}(
  # ...options as above...,
  :tls_sni_name => 'db.example.com',
  )

This requires MySQL client library 8.1 or higher. On older client libraries and all versions of MariaDB, passing this option raises ::Mysql2::Error rather than silently connecting without it.

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 Mysql2::Client.new().

caching_sha2_password and GnuTLS-linked client libraries

MySQL 8's default authentication plugin, caching_sha2_password, RSA-encrypts the password with the server's public key on a non-encrypted TCP connection. If you see this error:

{Mysql2::Error}: RSA Encryption not supported - caching_sha2_password plugin was built with GnuTLS support

your MariaDB Connector/C build can't take that step. Connector/C implements it for the OpenSSL and WinCrypt backends, not for GnuTLS. Debian and its derivatives ship a GnuTLS-linked mariadb-connector-c by default.

Suggested alternatives:

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:

development:
  adapter: mysql2
  encoding: utf8mb4
  database: my_db_name
  username: root
  password: my_password
  host: 127.0.0.1
  port: 3306
  flags:
    - -COMPRESS
    - FOUND_ROWS
    - MULTI_STATEMENTS
  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:

DATABASE_URL=mysql2://sql_user:sql_pass@sql_host_name:port/sql_db_name?option1=value1&option2=value2

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:

{Mysql2::Client.new}(:default_file => '/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.

{Mysql2::Client.new}(:init_command => "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 = {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

The call to client.query returns the first statement's result -- or nil, if that first statement doesn't produce one at all (e.g. CREATE TABLE or INSERT, same as outside of MULTI_STATEMENTS). This is still true if you pass :async => true: client.async_result also only returns the first statement's result.

The rest of the batch isn't deferred. The server runs every statement immediately, whether or not you ever call next_result. But you still have to loop over client.next_result/client.store_result, as shown above, to retrieve each later result or find out if a later statement errored.

Skip that loop and try to reuse the connection, and you'll get this error:

{Mysql2::Error}: Commands out of sync; you can't run this command now

Drain the loop to clear it. Or call client.abandon_results! to discard the remaining results without reading them.

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)

Cascading config

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)

or

# this will set the options for the {Mysql2::Result} instance returned from the {#execute} method
c = {Mysql2::Client.new}
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

Timezones

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 = {Mysql2::Client.new}
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 = {Mysql2::Client.new}
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).

The same applies to UNION results: MySQL widens a tinyint(1) column to tinyint(4) for any query combined with UNION, dropping the display-width attribute :cast_booleans depends on. There's no SQL-level fix either: a comparison like x = 1 comes back as a bigint, not a tinyint(1), so :cast_booleans won't catch that any more than the plain column does. The only reliable way to get a Ruby Boolean is to test the value in Ruby:

result = client.query("SELECT x FROM t1 UNION ALL SELECT x FROM t2")
result.each { |row| row['x'] = row['x'] == 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 = {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)

Character encoding

Pass :encoding to Mysql2::Client.new to set the connection's character set, as a MySQL/MariaDB charset name:

{Mysql2::Client.new}(:encoding => 'utf8mb4')

The default is utf8mb4. utf8mb4 is not the same as MySQL/MariaDB's own utf8, which is really utf8mb3 and can't hold 4-byte characters like most emoji; utf8mb4 can. See the MySQL and MariaDB docs for the full list of supported character sets and how they interact with column- and server-level collations.

Under :cast => false and :cast => :fast, values from numeric and date/time columns come back as ASCII-8BIT-encoded Strings. The connection's encoding only applies to text columns. Numeric and date/time values are always plain ASCII, so this is safe for concatenation, comparison, and interpolation with other ASCII-compatible character sets, including ISO-8859 and UTF-8. Ruby's Encoding::ASCII-8BIT and Encoding::Binary are aliases of one another; it's the same encoding used for BLOB, BINARY, and VARBINARY columns too.

Forcing a string encoding

Pass :force_encoding to Client#query or Statement#execute to retag string results with an encoding of your choosing:

result = client.query("SELECT * FROM legacy_table", force_encoding: {Encoding::UTF_8})

It accepts an Encoding object or an encoding name (anything Encoding.find accepts). Invalid values raise before anything is sent to the server.

Retag means exactly that: values keep their bytes and only the encoding tag changes — nothing is transcoded. Force means force, so the forced encoding wins over everything else: BLOB/BINARY columns are retagged too (instead of being tagged ASCII-8BIT), and the usual Encoding.default_internal conversion is skipped. This is useful for reading legacy data stored in a mislabeled character set (say, UTF-8 bytes living in latin1 columns), or for forcing binary when you want raw bytes for hashing or byte-wise comparison.

Only values that arrive as strings are affected. With the default cast: true, columns cast to Integer/Date/Time and friends are untouched; with cast: false, every non-NULL value is a string and all of them are retagged. Field names are never affected.

:force_encoding is fixed when the query or execute is issued — Mysql2::Result#each raises if you pass it there, because non-streaming Statement#execute materializes rows internally with #each, so a per-each value could never be honored consistently.

Partial casting

Between :cast => true and :cast => false sits :cast => :fast: cheap conversions still happen in C, while the expensive ones are skipped and their values returned as encoding-tagged Strings of the raw wire bytes.

result = client.query("SELECT * FROM table", :cast => :fast)

This is for callers that consume mysql2 results directly -- raw-mysql2 pipelines, ETL jobs, and applications that do their own value parsing -- where DECIMAL and temporal columns are often passed through or parsed lazily, and paying BigDecimal/Time construction for every cell up front is waste. Your code must be prepared to receive Strings for those columns. Note that Active Record does not use this option.

Any :cast value other than the exact symbol :fast (or false/nil) keeps meaning full casting. Prepared statement results are always fully cast, as with :cast => false.

Async

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.

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.

Streaming

::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:

Read more about the consequences of using mysql_use_result (what streaming is implemented with) here: https://dev.mysql.com/doc/c-api/9.7/en/mysql-use-result.html.

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.

Compatibility

This gem is tested with the following Ruby versions on Linux and macOS:

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

Ruby on Rails / Active Record

Asynchronous Active Record

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

Sequel

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

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

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.

Development

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.

I'm running an older version of Rails and need a back-ported feature

Requests to backport features, bug fixes, or newer MySQL/MariaDB compatibility to old mysql2 release lines can't be honored. Keeping old branches working would suggest they're properly supported and maintained when they aren't. An EOL Rails or Ruby version isn't receiving security patches either, and testing in CI becomes impossible over time as CI providers prune old runtime images.

Keeping an older application running means taking responsibility for its older open-source dependencies. For example, to use Rails 3.2 with a newer mysql2 gem:

  1. Fork Rails and set the needed version branch as the default, e.g. 3-2-stable</a>.
  2. Edit mysql2_adapter.rb</a> and change the gem 'mysql2', '~> 0.3.10' line to the needed version constraint.
  3. Point the Gemfile at the fork instead of the rails gem, using Bundler's git source.
  4. Test the combination in your actual dev, test, and production environments.

Special Thanks