Clarification about master slave configuration in mysql

Question

We are planning to migrate an existing MySQL database to a new server using the MySQL replication master slave procedure.

Unfortunately this will take a lot of time so we were thinking of doing a dump of the MySQL central db, restoring the dump on the new mysql db, and then setting up the master slave procedure.

Will using the master/slave procedure after restoring the dump of the original database overwrite the data on the new server, thereby wasting our time with the dump/restore process? Or will the master/slave procedure replicate the data that was added to the old server after the dump took place?

I am using MySQL 5.1 on Debian squeeze.

Answer 1

Yes, it will overwrite the data on the Slave. However, you can setup replication to pick up from the point-in-time of the dump and make it roll all changes since the dump was loaded on the Slave

For this Example, let's assume

• IP of the Master is 10.1.1.20
• IP of the Slave is 10.1.1.30

Here is what you do

STEP01 : Activate Binary Logging on the Old Server

Step01-a) Add this to /etc/my.cnf on the Master

[mysqld]
server-id=101120
log-bin=mysql-bin

Step01-b) # service mysql restart

After STEP01, you should see mysql-bin.000001 and mysql-bin.index in /var/lib/mysql

STEP02 : Perform mysqldump

On the Master, you can mysqldump the data and record from what point in time it happened.

# service mysql restart --skip-networking --skip-grants
# mysqldump --single-transaction --master-data=2 --all-databases --routines --triggers > MySQLData.sql
# service mysql restart

What this does is record the Master Log File and Position the moment the mysqldump started as a comment. You can visibly see it when you view line 22:

# head -22 MySQLData.sql | tail -1

STEP03 : Load the mysqldump into the Slave

Execute the mysql client loading the mysqldump into the Slave's mysql instance

# mysql -h10.1.1.30 -uroot -p < MySQLData.sql

STEP04 : Create MySQL Replication User on the Master

# mysql -uroot -p -e"GRANT REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO 'replicator'@'10.64.51.%' IDENTIFIED BY 'replpassword'"

STEP05 : Setup the Slave with a Separate Server ID

Add this to /etc/my.cnf on the Slave

[mysqld]
server-id=101130

and # service mysql restart

STEP06 : Setup the Replication on the Slave

Goto the mysql client and run the following command

mysql> CHANGE MASTER TO
    MASTER_HOST='10.1.1.20',
    MASTER_PORT=3306,
    MASTER_USER='replicator',
    MASTER_PASSWORD='replpassword',
    MASTER_LOG_FILE='mysql-bin.000001',
    MASTER_LOG_POS=1;

STEP07 : Setup the point-in-time Master Log and Position

Back in STEP02, I mentioned viewing the point-in-time position using

# head -22 MySQLData.sql | tail -1

You should see something like this:

#CHANGE MASTER TO MASTER_LOG_FILE='mysql-bin.000015', MASTER_LOG_POS=122957100;

Run it as command in the mysql client on the Slave

mysql> CHANGE MASTER TO MASTER_LOG_FILE='mysql-bin.000015', MASTER_LOG_POS=122957100;

Afterwards, run this command

mysql> SHOW SLAVE STATUS\G

You should see something like this:

*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 10.64.113.232
                  Master_User: replicant
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000015
          Read_Master_Log_Pos: 122957100
               Relay_Log_File: relay-bin.003666
                Relay_Log_Pos: 122957100
        Relay_Master_Log_File: mysql-bin.000015
             Slave_IO_Running: No
            Slave_SQL_Running: No
              Replicate_Do_DB:
          Replicate_Ignore_DB:
           Replicate_Do_Table:
       Replicate_Ignore_Table:
      Replicate_Wild_Do_Table:
  Replicate_Wild_Ignore_Table:
                   Last_Errno: 0
                   Last_Error:
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 106
              Relay_Log_Space: 106
              Until_Condition: None
               Until_Log_File:
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File:
           Master_SSL_CA_Path:
              Master_SSL_Cert:
            Master_SSL_Cipher:
               Master_SSL_Key:
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error:
               Last_SQL_Errno: 0
               Last_SQL_Error:
1 row in set (0.00 sec)

STEP08 : Launch Replication

Start up replication with this:

mysql> START SLAVE;

Afterwards, run this command again

mysql> SHOW SLAVE STATUS\G

If you see this

             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes

CONGRATULATIONS, MySQL Replication is Working !!!