What does failover mean in MySQL replication?

What does failover mean in MySQL replication?

The rest of the replication topology may also have to change – remaining replicas should change their master from the old, failed node to the newly chosen one. This process of “promoting” a replica to become a master after the old master has failed is called “failover”.

How does replication work in a MySQL server?

MySQL replication is a collective of nodes, each of them may serve one role at a time. It can become a master or a replica. There is only one master node at a given time. This node receives write traffic and it replicates writes to its replicas.

Why are MySQL replicas not logged in binary log?

Each MySQL replica ( Replica 1, Replica 2, and Replica 3) is a replica running with –log-bin and without enabling the log_slave_updates system variable. Because updates received by a replica from the source are not logged in the binary log unless log_slave_updates is enabled, the binary log on each replica is empty initially.

Why is MySQL replica running without log slave updates?

The reason for running the replica without log_slave_updates enabled is to prevent replicas from receiving updates twice in case you cause one of the replicas to become the new source. If Replica 1 has log_slave_updates enabled, it writes any updates that it receives from MySQL Source in its own binary log.

When does a replica become a master it is called?

This process of “promoting” a replica to become a master after the old master has failed is called “failover”. On the other hand, “switchover” happens when the user triggers the promotion of the replica.

Which is the master node in a replication cluster?

There is only one master node at a given time. This node receives write traffic and it replicates writes to its replicas. As you can imagine, being a single point of entry for data into the replication cluster, the master node is quite important.

How to change Replica 1 to master in MySQL?

On the replica Replica 1 being promoted to become the source, issue STOP REPLICA | SLAVE and RESET MASTER . On the other replicas Replica 2 and Replica 3, use STOP REPLICA | SLAVE and CHANGE REPLICATION SOURCE TO SOURCE_HOST=’Replica1′ or CHANGE MASTER TO MASTER_HOST=’Replica1′ (where ‘Replica1’ represents the real host name of Replica 1 ).

Why is MySQL replica running with–log-slave-updates = off?

The reason for running the replica with –log-slave-updates=OFF is to prevent replicas from receiving updates twice in case you cause one of the replicas to become the new source. If Replica 1 has –log-slave-updates enabled, which is the default, it writes any updates that it receives from Source in its own binary log.

How to stop the old master in MySQL?

Those scripts can be designed to use tools available in the particular environment to stop the old master.

When to run reset master on MySQL source?

During this procedure, do not forget to run RESET MASTER on MySQL Source before making Replica 1 , Replica 2, and Replica 3 replicas of MySQL Source. If you fail to do this, the replicas may pick up stale writes from the Web Client applications dating from before the point at which MySQL Source became unavailable.

What should I do if MySQL master becomes unavailable?

If for some reason MySQL Master becomes unavailable, you can pick one of the slaves to become the new master. For example, if you pick Slave 1, all Web Clients should be redirected to Slave 1, which writes the updates to its binary log. Slave 2 and Slave 3 should then replicate from Slave 1 .

Why is replication lag a problem in MySQL?

The problem with replication lag is that, when you promote a replica, you should reset the replication settings so it will not attempt to connect to the old master. This will also remove all relay logs, even if they are not yet applied – which leads to data loss.

What should I know about failover management software?

Most failover management software supports white and blacklists, which can be utilized to precisely define which replicas should or cannot be used as master candidates. A replication setup may be a mix of asynchronous and semi-synchronous replicas.

What happens to the old master when a failover is performed?

When a failover is performed the old master is, in some way, not reachable. It may have crashed, it may have suffered a network partitioning. It cannot be used at a given moment and its state is, typically, unknown.

Which is the best replication solution for MySQL?

MySQL Replication is probably the most popular high availability solution for MySQL, and widely used by top web properties like Twitter and Facebook. Although easy to set up, ongoing maintenance like software upgrades, schema changes, topology changes, failover and recovery have always been tricky. At least until MySQL 5.6.

What’s the difference between MySQL source and replica?

In this diagram, the MySQL Source holds the source database, the Replica hosts are replicas, and the Web Client machines are issuing database reads and writes. Web clients that issue only reads (and would normally be connected to the replicas) are not shown, as they do not need to switch to a new server in the event of failure.

What causes a client to fail to connect to a DNS server?

A client that receives a DNS SRV lookup result attempts to connect to the MySQL server on each of the listed hosts in order of preference, based on the priority and weighting assigned to each host by the DNS administrator. A failure to connect occurs only if the client cannot connect to any of the servers.

How does MySQL support DNS SRV records?

MySQL supports the use of DNS SRV records for connecting to servers. A client that receives a DNS SRV lookup result attempts to connect to the MySQL server on each of the listed hosts in order of preference, based on the priority and weighting assigned to each host by the DNS administrator.