The Ultimate Guide to High Availability with MariaDB

Replication Threads

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Contents

  1. Threads on the Master
    1. Binary Log Dump Thread
  2. Threads on the Slave
    1. Slave I/O Thread
    2. Slave SQL Thread
    3. Worker Threads

MariaDB's replication implementation requires several types of threads.

Threads on the Master

The master only has one type of replication-related thread: binary log dump thread.

Binary Log Dump Thread

The binary log dump thread runs on the master and dumps the binary log to the slave. In SHOW PROCESSLIST output, this thread is identified by Binlog Dump.

Threads on the Slave

The master has three types of replication-related threads: the slave I/O thread, the slave SQL thread, and worker threads, which are only applicable when parallel replication is in use.

Slave I/O Thread

The slave's I/O thread receives the binary log events from the master and writes them to its relay log.

Slave SQL Thread

The slave's SQL thread reads events from the relay log. What it does with them depends on whether parallel replication is in use. If parallel replication is not in use, then the SQL thread applies the events to its local copy of the data. If parallel replication is in use, then the SQL thread hands off the events to its worker threads to apply in parallel.

Worker Threads

When parallel replication is in use, then the SQL thread hands off the events to its worker threads to apply in parallel.

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