System variables are not replicated correctly when using
STATEMENT mode, except for the following
variables when they are used with session scope:
MIXED mode is used, the variables in the
preceding list, when used with session scope, cause a switch
from statement-based to row-based logging. See
Section 18.104.22.168, “Mixed Binary Logging Format”.
sql_mode is also replicated
except for the
NO_DIR_IN_CREATE mode; the
slave always preserves its own value for
of changes to it on the master. This is true for all replication
However, when mysqlbinlog parses a
SET @@sql_mode =
statement, the full
mode value, including
NO_DIR_IN_CREATE, is passed to
the receiving server. For this reason, replication of such a
statement may not be safe when
is in use.
read_only system variable
is not replicated. In addition, the enabling this variable has
different effects with regard to temporary tables, table
locking, and the
statement in different MySQL versions.
variable is not replicated. Increasing the value of this
variable on the master without doing so on the slave can lead
eventually to Table is full errors on the
slave when trying to execute
INSERT statements on a
MEMORY table on the master that is
thus permitted to grow larger than its counterpart on the slave.
For more information, see
Section 22.214.171.124, “Replication and MEMORY Tables”.
In statement-based replication, session variables are not replicated properly when used in statements that update tables. For example, the following sequence of statements will not insert the same data on the master and the slave:
SET max_join_size=1000; INSERT INTO mytable VALUES(@@max_join_size);
This does not apply to the common sequence:
SET time_zone=...; INSERT INTO mytable VALUES(CONVERT_TZ(..., ..., @@time_zone));
Replication of session variables is not a problem when row-based replication is being used, in which case, session variables are always replicated safely. See Section 17.1.2, “Replication Formats”.
In MySQL 5.5, the following session variables are written to the binary log and honored by the replication slave when parsing the binary log, regardless of the logging format:
Even though session variables relating to character sets and collations are written to the binary log, replication between different character sets is not supported.
It is strongly recommended that you always use the same setting
system variable on both master and slave. In particular, when a
case-sensitive file system is used, setting this variable to 1
on the slave, but to a different value on the master, can cause
two types of problems: Names of databases are not converted to
lowercase; in addition, when using row-based replication names
of tables are also not converted. Either of these problems can
cause replication to fail. This is a known issue, which is fixed
in MySQL 5.6.