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MySQL Monitor

MySQL Monitor is an application which continuously watches a MySQL database for data updates and publishes information about those changes to a message queue on RabbitMQ. It does this by connecting as a slave to the database and transforming the events which come through the replication log into JSON messages which are pushed to a publish/subscribe queue.

We built this system at Aventri to support highly scalable, near real-time data processing by multiple systems that rely on a central database. This application effectively lets you write the equivalent of database triggers in any programming language or system without adding any load to your master database. For example, make API calls triggered by data updates, or perform data transformations concurrently with multiple workers.

Requirements

We've included a docker configuration for easy setup and deployment. The docker-compose.yaml file will help you run a complete local environment for demonstration and testing.

The application has been tested with MySQL 5.6 and 5.7. Support for MySQL versions is dependent on the python-mysql-replication library.

The MySQL database the monitor connects to must have binary logging turned on. The binary log format must be ROW. For example,

; my.conf
server-id=1
log_bin=binlog
binlog_format=ROW
innodb_flush_log_at_trx_commit=1

The database must also have a user with slave replication permissions. This is the user to set in config.cfg.

GRANT REPLICATION SLAVE, REPLICATION CLIENT, SELECT ON *.* TO 'user'@'host';

Application Dependencies

Running the Monitor

The setup.sh script will copy config-example.cfg to config.cfg if it doesn't already exist. Set the MySQL and RabbitMQ connection parameters. Then run python mysql_monitor.py.

Building from docker/monitor/Dockerfile will do this for you.

How It Works

The MySQL Monitor is able to handle a high volume of data changes by separating its work into multiple processes. The "monitor" process listens to MySQL's binlog and pushes information about each event into an inter-process queue. The "processor" picks up the events and transforms each into one or more JSON messages which are pushed into the next inter-process queue. The "amqp" process keeps a persistent connection to RabbitMQ and enqueues the JSON messages.

The "amqp" process keeps an optional time-delay buffer used to remove duplicate messages. This can reduce the volume of messages when the same rows are repeatedly updated in a short period of time.

In the environment the monitor was originally built for, we've watched it easily handle hundreds of messages per second. The de-duping buffer reduced message volume by at least 10%.

The system will periodically save it's state to the data directory. This allows the monitor to continue from the last binlog position it processed after being restarted. The current binlog position is only recorded after the related messages are sent to RabbitMQ. This guarantees no data is lost if the connection to RabbitMQ is dropped.

Messages

Heartbeat

{
    "timestamp": 1539710711, 
    "type": "heartbeat"
}

Insert row

{
    "timestamp": 1539710711, 
    "binlog_timestamp": 1539710709, 
    "type": "row_insert"
    "table_name": "employee", 
    "keys": {
        "id": 2760
    }, 
    "values": {
        "fname": "abc", 
        "lname": "def", 
        "id": 2760
    },
}

Update row

{
    "timestamp": 1539710711, 
    "binlog_timestamp": 1539710709, 
    "type": "row_update",
    "table_name": "employee", 
    "keys": {
        "id": 1903
    }, 
    "before_values": {
        "fname": "Ldurlqgfqv"
    },
    "after_values": {
        "fname": "Ldurlqgfqvsdf"
    }
}

Delete row

{
    "timestamp": 1539710711, 
    "binlog_timestamp": 1539710709, 
    "type": "row_delete", 
    "table_name": "employee", 
    "keys": {
        "id": 5
    }
}