MySQL replication works for InnoDB tables as
it does for MyISAM tables. It is also
possible to use replication in a way where the storage engine on
the slave is not the same as the original storage engine on the
master. For example, you can replicate modifications to an
InnoDB table on the master to a
MyISAM table on the slave.
To set up a new slave for a master, you have to make a copy of
the InnoDB tablespace and the log files, as
well as the .frm files of the
InnoDB tables, and move the copies to the
slave. If the innodb_file_per_table variable
is enabled, you must also copy the .ibd
files as well. For the proper procedure to do this, see
Section 13.6.8, “Backing Up and Recovering an InnoDB Database”.
If you can shut down the master or an existing slave, you can
take a cold backup of the InnoDB tablespace
and log files and use that to set up a slave. To make a new
slave without taking down any server you can also use the
commercial
InnoDB
Hot Backup tool.
Transactions that fail on the master do not affect replication
at all. MySQL replication is based on the binary log where MySQL
writes SQL statements that modify data. A transaction that fails
(for example, because of a foreign key violation, or because it
is rolled back) is not written to the binary log, so it is not
sent to slaves. See Section 12.4.1, “START TRANSACTION, COMMIT, and
ROLLBACK Syntax”.
Replication and CASCADE.
Cascading actions for InnoDB tables on the
master are replicated to the slave only
if both the master's and slave' versions of the
tables sharing the foreign key relation use
InnoDB. This is true whether you are using
statement-based or row-based replication. For example, suppose
you have started replication, and then create two tables on
the master using the following CREATE TABLE
statements:
CREATE TABLE fc1 (
i INT PRIMARY KEY,
j INT
) ENGINE = InnoDB;
CREATE TABLE fc2 (
m INT PRIMARY KEY,
n INT,
FOREIGN KEY ni (n) REFERENCES fc1 (i)
ON DELETE CASCADE
) ENGINE = InnoDB;
Suppose that the slave does not have InnoDB
support enabled. If this is the case, then the tables on the
slave are created, but they use the MyISAM
storage engine, and the FOREIGN KEY option
is ignored. Now we insert some rows into the tables on the
master:
master>INSERT INTO fc1 VALUES (1, 1), (2, 2);Query OK, 2 rows affected (0.09 sec) Records: 2 Duplicates: 0 Warnings: 0 master>INSERT INTO fc2 VALUES (1, 1), (2, 2), (3, 1);Query OK, 3 rows affected (0.19 sec) Records: 3 Duplicates: 0 Warnings: 0
At this point, on both the master and the slave, table
fc1 contains 2 rows, and table
fc2 contains 3 rows, as shown here:
master>SELECT * FROM fc1;+---+------+ | i | j | +---+------+ | 1 | 1 | | 2 | 2 | +---+------+ 2 rows in set (0.00 sec) master>SELECT * FROM fc2;+---+------+ | m | n | +---+------+ | 1 | 1 | | 2 | 2 | | 3 | 1 | +---+------+ 3 rows in set (0.00 sec) slave>SELECT * FROM fc1;+---+------+ | i | j | +---+------+ | 1 | 1 | | 2 | 2 | +---+------+ 2 rows in set (0.00 sec) slave>SELECT * FROM fc2;+---+------+ | m | n | +---+------+ | 1 | 1 | | 2 | 2 | | 3 | 1 | +---+------+ 3 rows in set (0.00 sec)
Now suppose that you perform the following
DELETE statement on the master:
master> DELETE FROM fc1 WHERE i=1;
Query OK, 1 row affected (0.09 sec)
Due to the cascade, table fc2 on the master
now contains only 1 row:
master> SELECT * FROM fc2;
+---+---+
| m | n |
+---+---+
| 2 | 2 |
+---+---+
1 row in set (0.00 sec)
However, the cascade does not propagate to the slave. The
slave's copy of fc2 still contains all
of the rows that were originally inserted:
slave> SELECT * FROM fc2;
+---+---+
| m | n |
+---+---+
| 1 | 1 |
| 3 | 1 |
| 2 | 2 |
+---+---+
3 rows in set (0.00 sec)
This difference is due to the fact that the cascading deletes
are handled internally by the InnoDB
storage engine, which means that none of the changes are
logged.

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