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Replication and Master or Slave Shutdowns

It is safe to shut down a master server and restart it later. When a slave loses its connection to the

master, the slave tries to reconnect immediately and retries periodically if that fails. The default is to

retry every 60 seconds. This may be changed with the CHANGE MASTER TO statement. A slave also

is able to deal with network connectivity outages. However, the slave notices the network outage only

after receiving no data from the master for slave_net_timeout [2029] seconds. If your outages are

short, you may want to decrease slave_net_timeout [2029], See Section 5.1.4.

"Server System

Variables”.

An unclean shutdown (for example, a crash) on the master side can result in the master binary log

having a finał position less than the most recent position read by the slave, due to the master binary log

file not being flushed. This can cause the slave not to be able to replicate when the master comes back

up. Setting sync_binlog=l [2055] in the master my. cnf file helps to minimize this problem because

it causes the master to flush its binary log morę frequently.

Shutting down a slave cleanly is safe because it keeps track of where it left off. However, be ca refu I

that the slave does not have temporary tables open; see Section 16.4.1.22, "Replication and

Temporary Tables". Unclean shutdowns might produce problems, especially if the disk cache was not

flushed to disk before the problem occurred:

•    For transactions, the slave commits and then updates relay-log. info. If a crash occurs between

these two operations, relay log Processing will have proceeded further than the information file

indicates and the slave will re-execute the events from the last transaction in the relay log after it has been restarted.

•    A similar problem can occur if the slave updates relay-log. info but the server host

crashes before the write has been flushed to disk. To minimize the chance of this occurring,

set sync_relay_log_inf o=l [2036] in the slave my. cnf file. The default value of

sync_relay_log_info [2036] is 0, which does not cause writes to be forced to disk; the server

relies on the operating system to flush the file from time to time.

The fault tolerance of your system for these types of problems is greatly increased if you have a good uninterruptible power supply.