The following sections contain information about mysqld options and server variables that are used in replication and for controlling the binary log. Options and variables for use on replication masters and replication slaves are covered separately, as are options and variables relating to binary logging. A set of quick-reference tables providing basic information about these options and variables is also included.
Of particular importance is the
|System Variable Name|
This option is common to both master and slave replication servers, and is used in replication to enable master and slave servers to identify themselves uniquely. For additional information, see Section 126.96.36.199, “Replication Master Options and Variables”, and Section 188.8.131.52, “Replication Slave Options and Variables”.
On the master and each slave, you must use the
--server-id option to establish a
unique replication ID in the range from 1 to
232 – 1. “Unique”,
means that each ID must be different from every other ID in use by
any other replication master or slave. For example,
If you omit
--server-id, the default
ID is 0, in which case the master refuses connections from all
slaves, and slaves refuse to connect to the master. In MySQL
5.6, whether the server ID is set to 0 explicitly or
the default is allowed to be used, the server sets the
server_id system variable to 1; this is a known
issue that is fixed in MySQL 5.7.
For more information, see Section 184.108.40.206, “Setting the Replication Slave Configuration”.
|System Variable Name|
When starting, the MySQL server automatically obtains a UUID as follows:
auto.cnf file has a format similar to that
files. In MySQL 5.6,
only a single
[auto] section containing a single
server_uuid setting and value; the
file's contents appear similar to what is shown here:
auto.cnf file is automatically generated;
do not attempt to write or modify this file.
Also beginning with MySQL 5.6, when using MySQL replication, masters
and slaves know one another's UUIDs. The value of a
slave's UUID can be seen in the output of
SHOW SLAVE HOSTS. Once
START SLAVE has been executed (but
not before), the value of the master's UUID is available on the
slave in the output of
In MySQL 5.6.5 and later, a server's
server_uuid is also used in GTIDs for
transactions originating on that server. For more information, see
Section 17.1.3, “Replication with Global Transaction Identifiers”.
When starting, the slave I/O thread generates an error and aborts if
its master's UUID is equal to its own unless the
--replicate-same-server-id option has
been set. In addition, the slave I/O thread generates a warning if
either of the following is true:
The addition of the
system variable in MySQL 5.6 does not change the
requirement for setting a unique
--server-id for each MySQL server
as part of preparing and running MySQL replication, as described
earlier in this section.