slave重新指向新的master 的关键日志输出，通过这些日志输出，我们大致可以明白MMM自动failover或在线切换时的执行流程。
--自动failover，slave节点
2015/02/06 01:47:09? INFO Changing active master to 'raugherdb1'
2015/02/06 01:47:09 DEBUG Executing /usr/lib/mysql-mmm//agent/set_active_master raugherdb1
2015/02/06 01:47:09 DEBUG Result: OK
--在线切换
--主1节点
2015/02/06 05:49:23 DEBUG Received Command SET_STATUS|1|raugherdb1|ONLINE|reader(10.5.6.103)|raugherdb2
2015/02/06 05:49:23? INFO We have some new roles added or old rules deleted!
2015/02/06 05:49:23? INFO Deleted: writer(10.5.6.100)
2015/02/06 05:49:23 DEBUG Executing /usr/lib/mysql-mmm//agent/mysql_deny_write?
2015/02/06 05:49:23 DEBUG Executing /usr/lib/mysql-mmm//agent/clear_ip eth0 10.5.6.100
?
--主2节点
2015/02/06 05:49:22 DEBUG Daemon: Command = 'SET_STATUS|1|raugherdb2|ONLINE|reader(10.5.6.101),writer(10.5.6.100)|raugherdb2'
2015/02/06 05:49:22 DEBUG Received Command SET_STATUS|1|raugherdb2|ONLINE|reader(10.5.6.101),writer(10.5.6.100)|raugherdb2
2015/02/06 05:49:22? INFO We have some new roles added or old rules deleted!
2015/02/06 05:49:22? INFO Added:? writer(10.5.6.100)
2015/02/06 05:49:22 DEBUG Executing /usr/lib/mysql-mmm//agent/sync_with_master?
2015/02/06 05:49:23 DEBUG Executing /usr/lib/mysql-mmm//agent/mysql_allow_write?
2015/02/06 05:49:23 DEBUG Executing /usr/lib/mysql-mmm//agent/configure_ip eth0 10.5.6.100
?
--slave节点
2015/02/06 05:49:22 DEBUG Daemon: Command = 'SET_STATUS|1|raugherdb|ONLINE|reader(10.5.6.102)|raugherdb2'
2015/02/06 05:49:22 DEBUG Received Command SET_STATUS|1|raugherdb|ONLINE|reader(10.5.6.102)|raugherdb2
2015/02/06 05:49:22? INFO Changing active master to 'raugherdb2'
2015/02/06 05:49:22 DEBUG Executing /usr/lib/mysql-mmm//agent/set_active_master raugherdb2
2015/02/06 05:49:23 DEBUG Result: OK
以下是set_active_master方法的代码：
sub set_active_master($) {
? ? my $new_peer = shift;
? ? _exit_error('Name of new master is missing') unless (defined($new_peer));
?
? ? my $this = _get_this();
?
? ? _exit_error('New master is equal to local host!?') if ($this eq $new_peer);
?
? ? # Get local connection info
? ? my ($this_host, $this_port, $this_user, $this_password) = _get_connection_info($this);
? ? _exit_error("No connection info for local host '$this_host'") unless defined($this_host);
? ? ?
? ? # Get connection info for new peer
? ? my ($new_peer_host, $new_peer_port, $new_peer_user, $new_peer_password) = _get_connection_info($new_peer);
? ? _exit_error("No connection info for new peer '$new_peer'") unless defined($new_peer_host);
? ? ?
? ? # Connect to local server
? ? my $this_dbh = _mysql_connect($this_host, $this_port, $this_user, $this_password);
? ? _exit_error("Can't connect to MySQL (host = $this_host:$this_port, user = $this_user)! " . $DBI::errstr) unless ($this_dbh);
?
? ? # Get slave info
? ? my $slave_status = $this_dbh->selectrow_hashref('SHOW SLAVE STATUS');
? ? _exit_error('SQL Query Error: ' . $this_dbh->errstr) unless defined($slave_status);
?
? ? my $wait_log? = $slave_status->{Master_Log_File};
? ? my $wait_pos? = $slave_status->{Read_Master_Log_Pos};
?
? ? my $old_peer_ip? ? = $slave_status->{Master_Host};
? ? _exit_error('No ip for old peer') unless ($old_peer_ip);
?
? ? # Get connection info for old peer
? ? my $old_peer = _find_host_by_ip($old_peer_ip);
? ? _exit_error('Invalid master host in show slave status') unless ($old_peer);
?
? ? _exit_ok('We are already a sla