MySQL Replicator

MysqlReplicator gem is a library for processing MySQL Binlog events with MySQL Replication Protocol.

And also, this is lightweight because only depend on the Ruby standard library.

Support version

• MySQL >= 8.0
• Ruby >= 3.3

Installation

Install the gem and add to the application's Gemfile by executing:

bundle add mysql_replicator

You can of course add a gem call in your Gemfile yourself.

gem 'mysql_replicator'

If bundler is not being used to manage dependencies, install the gem by executing:

gem install mysql_replicator

Usage

Run with convenience method.

# `run` method: Connect to MySQL server, and start to handle replication event
MysqlReplicator.run(
  host: 'your_mysql_host', # default localhost
  port: 3307,              # default 3306
  user: 'username',        # default root
  password: 'password',    # default empty string
  database: 'test'         # default empty string
) do |binlog_event|
  # write code to process binlog event
end

Or run with interface manually.

# create connection to MySQL server
conn = MysqlReplicator::Connection.new(
  host: 'your_mysql_host', # default localhost
  port: 3307,              # default 3306
  user: 'username',        # default root
  password: 'password',    # default empty string
  database: 'test'         # default empty string
)
# create binlog client
client = MysqlReplicator::BinlogClient.new(conn)
# set binlog event handler
client.on do |binlog_event|
  # write code to process binlog event
end
# start replication
client.start_replication

If you run a create table and insert query.

CREATE TABLE users (
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(255),
  PRIMARY KEY (id)
);

INSERT INTO users VALUES ('alice');

MysqlReplicator received binlog_event with :WRITE_ROWS event.
When INSERT query, you can get inserted row data.

puts binlog_event
# =>
{
  timestamp: "2025-12-01 12:00:00",
  event_type: :WRITE_ROWS,
  server_id: 1,
  execution: {
    table_id: 10,
    flags: 0,
    extra_data_length: 0,
    column_count: 2,
    rows: [
      {
         ordinal_position: 1,
         data_type: 'int',
         column_name: 'id',
         value: 1,
         primary_key: true
      },
      {
         ordinal_position: 2,
         data_type: 'varchar',
         column_name: 'name',
         value: 'alice',
         primary_key: false
      }
    ]
  }
}

If you run the update query.

UPDATE users SET name = 'bob' WHERE id = 1;

MysqlReplicator received binlog_event with :UPDATE_ROWS event.
When UPDATE query, you can get row data before and after the change.

puts binlog_event
# =>
{
  timestamp: "2025-12-01 12:01:00",
  event_type: :UPDATE_ROWS,
  server_id: 1,
  execution: {
    table_id: 10,
    flags: 0,
    extra_data_length: 0,
    column_count: 2,
    rows: [
      {
        before: [
          {
            ordinal_position: 1,
            data_type: 'int',
            column_name: 'id',
            value: 1,
            primary_key: true
          },
          {
            ordinal_position: 2,
            data_type: 'varchar',
            column_name: 'name',
            value: 'alice', # before name
            primary_key: false
          }
        ],
        after: [
          {
            ordinal_position: 1,
            data_type: 'int',
            column_name: 'id',
            value: 1,
            primary_key: true
          },
          {
            ordinal_position: 2,
            data_type: 'varchar',
            column_name: 'name',
            value: 'bob', # after name
            primary_key: false
          }
        ]
      }
    ]
  }
}

If you run the delete query.

DELETE FROM users WHERE id = 1;

MysqlReplicator received binlog_event with :DELETE_ROWS event.
When DELETE query, you can get row data before and after the change.

puts binlog_event
# =>
{
  timestamp: "2025-12-01 12:02:00",
  event_type: :DELETE_ROWS,
  server_id: 1,
  execution: {
    table_id: 10,
    flags: 0,
    extra_data_length: 0,
    column_count: 2,
    rows: [
      {
         ordinal_position: 1,
         data_type: 'int',
         column_name: 'id',
         value: 1,
         primary_key: true
      },
      {
         ordinal_position: 2,
         data_type: 'varchar',
         column_name: 'name',
         value: 'bob',
         primary_key: false
      }
    ]
  }
}

If you want to use your custom logger.

# Custom logger available
MysqlReplicator.logger = your_custom_logger

Supported event

Event type
ROTATE_EVENT	✅
FORMAT_DESCRIPTION_EVENT	✅
QUERY_EVENT	✅
TABLE_MAP_EVENT	✅
WRITE_ROWS_EVENT (V2)	✅
UPDATE_ROWS_EVENT (V2)	✅
DELETE_ROWS_EVENT (V2)	✅
XID_EVENT	✅
GTID_LOG_EVENT	❌
PREVIOUS_GTIDS_LOG_EVENT	❌
HEARTBEAT_LOG_EVENT	❌
STOP_EVENT	❌

Supported MySQL data type

Numeric type

MySQL type
TINYINT	✅
SMALLINT	✅
MEDIUMINT	✅
INT	✅
BIGINT	✅
FLOAT	✅
DOUBLE	✅
DECIMAL	✅
BIT	❌

String type

MySQL type
CHAR	✅
VARCHAR	✅
TINYTEXT	✅
TEXT	✅
MEDIUMTEXT	✅
LONGTEXT	✅
ENUM	✅
SET	❌

Binary type

MySQL type
BINARY	✅
VARBINARY	✅
TINYBLOB	✅
BLOB	✅
MEDIUMBLOB	✅
LONGBLOB	✅

Date and Time type

MySQL type
DATE	✅
TIME	✅
DATETIME	✅
TIMESTAMP	✅
YEAR	❌

Special type

MySQL type
JSON	✅
GEOMETRY	❌

Supported Binary JSON value type

JSON value type
SMALL_OBJECT	✅
LARGE_OBJECT	✅
SMALL_ARRAY	✅
LARGE_ARRAY	✅
LITERAL (null / true / false)	✅
INT16	✅
UINT16	✅
INT32	✅
UINT32	✅
INT64	✅
UINT64	✅
DOUBLE	✅
STRING	✅
OPAQUE	❌

Development

Start MySQL server.

$ docker compose up

Start MysqlReplicator to check if local code works.

irb(main):001> MysqlReplicator.run(database: 'test') { |evt| puts evt }

Submit sample DDL and query to MySQL server. Check spec/supports/sql.

Run spec for test.

$ bundle exec rspec

Run rubocop for linter.

$ bundle exec rubocop

Run steep for type check.

$ bundle exec steep check

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/waka/mysql_replicator. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the MysqlReplicator project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.