How Does MySQL Replication Works?

See the bellow image, it represents how asynchronous replication works on MySQL
How replication works

Bearing in mind the number on the image, let’s see how the process works:

  • Item 1 in the image represents the clients executing queries on master, note that the master is capable to handle multiple simultaneous connections (it can be configurable by max_connections variable). 
  • Master process these queries, and save it to his binary log(item number 2 in the image), then it can later on be replied on the slave.
  • The slave has 2 threads reubuntu mount ext4 partitionsponsible to deal with replication :

    • IO_THREAD – is responsible to connect to the Master, ask for new transaction (item number 3 in the image) and save them to his own log (relay log, item number 4 in the image).

    • SQL_THREAD – is responsible for read all new transaction from relay log(item number 5 in the image), and apply them to the database server(item number 6 in the image) .

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