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 22.214.171.124, “Replication Master Options and Variables”, and Section 126.96.36.199, “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,
--server-id option must be specified if binary
logging is enabled, otherwise the server is not allowed to start. If
the server ID is set to 0, binary logging takes place, but a master
with a server ID of 0 refuses any connections from slaves, and a
slave with a server ID of 0 refuses to connect to a master. (Bug
#11763963, Bug #56739)
For more information, see Section 188.8.131.52.1, “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 16.1.3, “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: