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 and global transaction identifiers (GTIDs). A set of quick-reference tables providing basic information about these options and variables is also included.
Of particular importance is the
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 184.108.40.206, “Replication Master Options and Variables”, and Section 220.127.116.11, “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,
In MySQL 5.7.2 and earlier, if you start a master server without
--server-id to set its ID, the
default ID is 0. In this case, the master refuses connections from
all slaves, slaves refuse to connect to the master, and the server
server_id system variable
to 1. In MySQL 5.7.3 and later, the
must be used if binary logging is enabled, and a value of 0 is not
changed by the server. If you specify
--server-id without an argument, the
effect is the same as using 0. In either case, if the
server_id is 0, binary logging takes place, but
slaves cannot connect to the master, nor can any other servers
connect to it as slaves. (Bug #11763963, Bug #56718)
For more information, see Section 18.104.22.168, “Setting the Replication Slave Configuration”.
The presence of the
system variable in MySQL 5.7 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.
When starting, the MySQL server automatically obtains a UUID as follows:
auto.cnf file has a format similar to that
files. In MySQL 5.7,
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.
When using MySQL replication, masters and slaves know each
other'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, the
value of the master's UUID is available on the slave in the
SHOW SLAVE STATUS.
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: