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(mysql.info)Replication Intro

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Introduction
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One way replication can be used is to increase both robustness and
speed. For robustness you can have two systems and can switch to the
backup if you have problems with the master. The extra speed is
achieved by sending a part of the non-updating queries to the replica
server. Of course this only works if non-updating queries dominate, but
that is the normal case.

Starting in Version 3.23.15, MySQL supports one-way replication
internally. One server acts as the master, while the other acts as the
slave. Note that one server could play the roles of master in one pair
and slave in the other. The master server keeps a binary log of updates
(Note: Binary log.) and an index file to binary logs to keep track of
log rotation.  The slave, upon connecting, informs the master where it
left off since the last successfully propagated update, catches up on
the updates, and then blocks and waits for the master to notify it of
the new updates.

Note that if you are replicating a database, all updates to this
database should be done through the master!

Another benefit of using replication is that one can get live backups of
the system by doing a backup on a slave instead of doing it on the
master. Note: Backup.