How to re-sync the Mysql DB if Master and slave have different database incase of Mysql replication?

Question

Mysql Server1 is running as MASTER.
Mysql Server2 is running as SLAVE.

Now DB replication is happening from MASTER to SLAVE.

Server2 is removed from network and re-connet it back after 1 day. After this there is mismatch in database in master and slave.

How to re-sync the DB again as after restoring DB taken from Master to Slave also doesn't solve the problem ?

Answer 1

Hello! I think, Maatkit utilits helps for you! You can use mk-table-sync. Please see this link: http://www.maatkit.org/doc/mk-table-sync.html

Answer 2

Unless you are writing directly to the slave (Server2) the only problem should be that Server2 is missing any updates that have happened since it was disconnected. Simply restarting the slave with "START SLAVE;" should get everything back up to speed.

Answer 3

Here is what I typically do when a mysql slave gets out of sync. I have looked at mk-table-sync but thought the Risks section was scary looking.

On Master:

SHOW MASTER STATUS

The outputted columns (File, Position) will be of use to us in a bit.

On Slave:

STOP SLAVE

Then dump the master db and import it to the slave db.

Then run the following:

CHANGE MASTER TO
  MASTER_LOG_FILE='[File]',
  MASTER_LOG_POS=[Position];
START SLAVE;

Where [File] and [Position] are the values outputted from the "SHOW MASTER STATUS" ran above.

Hope this helps!

Answer 4

This is the full step-by-step procedure to resync a master-slave replication from scratch:

At the master:

RESTART MASTER;
FLUSH TABLES WITH READ LOCKS;
SHOW MASTER STATUS;

And copy the values of the result of the last command somewhere.

Wihtout closing the connection to the client (because it would release the read lock) issue the command to get a dump of the master:

mysqldump -uroot -p --all-database > /a/path/mysqldump.sql

Now you can release the lock, even if the dump hasn't end. To do it perform the following command in the mysql client:

UNLOCK TABLES;

Now copy the dump file to the slave using scp or your preferred tool.

At the slave:

Load master's data dump:

mysql -uroot -p < mysqldump.sql

Open a connection to mysql and type:

STOP SLAVE;
RESET SLAVE;
CHANGE MASTER TO MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=98;

Where the values of the above fields are the ones you copied before.

Finally type

START SLAVE;

And to check that everything is working again, if you type

SHOW SLAVE STATUS;

you should see:

Slave_IO_Running: Yes
Slave_SQL_Running: Yes

That's it!