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(mysql.info)Replication Implementation

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Replication Implementation Overview
-----------------------------------

MySQL replication is based on the server keeping track of all changes
to your database (updates, deletes, etc) in the binary log. (Note:
Binary log.) and the slave server(s) reading the saved queries from
the master server's binary log so that the slave can execute the same
queries on its copy of the data.

It is *very important* to realize that the binary log is simply a
record starting from a fixed point in time (the moment you enable binary
logging). Any slaves which you set up will need copies of all the data
from your master as it existed the moment that you enabled binary
logging on the master. If you start your slaves with data that doesn't
agree with what was on the master *when the binary log was started*,
your slaves may fail.

A future version (4.0) of MySQL will remove the need to keep a
(possibly large) snapshot of data for new slaves that you might wish to
set up through the live backup functionality with no locking required.
However, at this time, it is necessary to block all writes either with a
global read lock or by shutting down the master while taking a snapshot.

Once a slave is properly configured and running, it will simply connect
to the master and wait for updates to process. If the master goes away
or the slave loses connectivity with your master, it will keep trying to
connect every `master-connect-retry' seconds until it is able to
reconnect and resume listening for updates.

Each slave keeps track of where it left off. The master server has no
knowledge of how many slaves there are or which ones are up-to-date at
any given time.

The next section explains the master/slave setup process in more detail.