# mysql\_replication

**URL:** <https://community.netdata.cloud/t/mysql-replication/2288>\
**Category:** Alerts\
**Created:** [December 10, 2021, 8:08am UTC](https://community.netdata.cloud/t/mysql-replication/2288 "2021-12-10T08:08:09Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Ancairon](https://yyz1.discourse-cdn.com/flex029/user_avatar/community.netdata.cloud/ancairon/32/1001_2.png) [@Ancairon](https://community.netdata.cloud/u/Ancairon)\
**Post date:** [December 10, 2021, 8:08am UTC](https://community.netdata.cloud/t/mysql-replication/2288/1 "2021-12-10T08:08:09Z")

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# mysql\_replication

## Database | MySQL, MariaDB

This alert monitors the replication status of the MySQL server.  
If you receive this, either both or one of the I/O and SQL threads are not running.

This alert is raised into critical if replication has stopped.

> In MySQL, replication involves the source database writing down every change made to the data  
> held within one or more databases in a special file known as the binary log. Once the replica  
> instance has been initialized, it creates two threaded processes. The first, called the IO  
> thread, connects to the source MySQL instance and reads the binary log events line by line,  
> and then copies them over to a local file on the replica’s server called the relay log. The  
> second thread, called the SQL thread, reads events from the relay log and then applies them  
> to the replica instance as fast as possible.
> 
> Recent versions of MySQL support two methods for replicating data. The difference between these  
> replication methods has to do with how replicas track which database events from the source  
> they’ve already processed.[1](https://www.digitalocean.com/community/tutorials/how-to-set-up-replication-in-mysql)

For further information, please have a look at the _References and Sources_ section.

> **References and Sources**
>
> 1. [Replication in MySQL](https://www.digitalocean.com/community/tutorials/how-to-set-up-replication-in-mysql)
> 2. [MySQL documentation](https://dev.mysql.com/doc/refman/5.7/en/replication-administration-status.html)
> 3. [Section 8.14.6, “Replication Replica I/O  
> Thread States”](https://dev.mysql.com/doc/refman/5.7/en/replica-io-thread-states.html)
> 4. [Section 8.14.7, “Replication Replica SQL Thread  
> States”](https://dev.mysql.com/doc/refman/5.7/en/replica-sql-thread-states.html)

### Troubleshooting Section

> **Check which thread is not running**
>
> From the MySQL command line you can run:
> 
> - For MySQL and MariaDB before v10.2.0:
> 
> - For MariaDB v10.2.0+:
> 
> This will show you three important rows among other info:
> 
> > - Slave\_IO\_State:  
> > The current status of the replica. See [Section 8.14.6, “Replication Replica I/O  
> > Thread States”](https://dev.mysql.com/doc/refman/5.7/en/replica-io-thread-states.html), and  
> > [Section 8.14.7, “Replication Replica SQL Thread  
> > States”](https://dev.mysql.com/doc/refman/5.7/en/replica-sql-thread-states.html), for more  
> > information.
> > 
> > - Slave\_IO\_Running:  
> > Whether the I/O thread for reading the source’s binary log is running.  
> > Normally, you want this to be **Yes** unless you have not yet started replication or have  
> > explicitly stopped it with STOP SLAVE.
> > 
> > - Slave\_SQL\_Running:  
> > Whether the SQL thread for executing events in the relay log is running. As  
> > with the I/O thread, this should normally be **Yes**. [2](https://dev.mysql.com/doc/refman/5.7/en/replication-administration-status.html)
> 
> For more info you can refer to the [MySQL documentation](https://dev.mysql.com/doc/refman/5.7/en/replication-administration-status.html).