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Using the topology you mentioned from the MySQL Documentation

Let's setup the first scenario

EXAMPLE IPs for Each DB Server

• Master1 : 10.20.30.40
• Master2 : 10.20.30.50
• Slave_1 : 10.20.30.60
• replication user is repluser@'%'
• replication password is replpass

Make sure binary logging is enabled on all the Slaves

We will do the following

• Promote Master2 to Master1
• Promote Slave_1 to Master2
• Demote Master1 to Slave1

Step 01 : On Master2, run the following

mysql> SET GLOBAL read_only = 1;
mysql> STOP SLAVE;
mysql> RESET SLAVE;
mysql> CHANGE MASTER TO master_host='';
mysql> FLUSH TABLES;
mysql> SET GLOBAL read_only = 0;

Step 02 : Move your CNAME/VIP to Master2

Step 03 : On Slave_1, run mysql> RESET MASTER; FLUSH TABLES;

Step 04 : On Slave_1, dump the data

NEW_MASTER_HOST="10.20.30.60"
MYSQL_USER=root
MYSQL_PASS=rootpassword
MYSQL_CONN="-u${MYSQL_USER} -p${MYSQL_PASS}"
MYSQLDUMP_OPTIONS="--single-transaction"
MYSQLDUMP_OPTIONS="${MYSQLDUMP_OPTIONS} --routines"
MYSQLDUMP_OPTIONS="${MYSQLDUMP_OPTIONS} --triggers"
MYSQLDUMP_OPTIONS="${MYSQLDUMP_OPTIONS} --master-data=1"
MYSQLDUMP_OPTIONS="${MYSQLDUMP_OPTIONS} --all-databases"
echo "STOP SLAVE;" > MySQLData.sql
echo "CHANGE MASTER TO master_host='${NEW_MASTER_IP}'," >> MySQLData.sql
echo "master_port=3306," >> MySQLData.sql
echo "master_user='repluser'," >> MySQLData.sql
echo "master_password='replpass'," >> MySQLData.sql
echo "master_log_file='bogus'," >> MySQLData.sql
echo "master_log_pos=1;" >> MySQLData.sql
mysqldump ${MYSQL_CONN} ${MYSQLDUMP_OPTIONS} >> MySQLData.sql
echo "START SLAVE;" >> MySQLData.sql
gzip MySQLData.sql

Step 05 : When Master1 comes back up, rsync or scp MySQLData.sql.gz from Slave_1 to Master1

Step 06 : Login to MySQL on the Master1 and setup it up to replicate from Slave_1

Don't worry about the real binary log filename and position.

Using --master-data=1 embeds CHANGE MASTER TO command with the real coordinates on line 23 of a standard dump.

You can see it with the following

less MySQLData.sql.gz | head -35 | tail -1

Step 07 : Load the data into Master1

MYSQL_USER=root
MYSQL_PASS=rootpassword
MYSQL_CONN="-u${MYSQL_USER} -p${MYSQL_PASS}"
gzip -d < MySQLData.sql.gz | mysql ${MYSQL_CONN}

Step 08 : Login to MySQL on Master1

mysql> SHOW SLAVE STATUS\G

and Make sure Slave_IO_Running and Slave_SQL_Running both say Yes

#EPILOGUE

When Done, the topology should be

• Master1 : 10.20.30.60
• Master2 : 10.20.30.50
• Slave_1 : 10.20.30.40

#DISCLAIMER

Please try this out on Test Servers before deploying to Production

#GIVE IT A TRY !!!

Note: I would advise that you have multiples slaves

• One for Nightly Backups
• The others for load balancing SELECTs