Mysql – Best database replication technique for a very unstable (power wise) network

As long as the traveling user will be adding, updating, and deleting records and can guarantee that no one else is touching in the master, there is something you can try.

What you want to do is setup MySQL Circular Replication (Master/Master) between Master and LapTop. Once you have this esatblished and the time has come for the traveling user (TVU) to leave for the week, here is what to do:

Step 1 : Run STOP SLAVE; on the Master

Step 2 : Run STOP SLAVE; on the LapTop

Step 3 : TVU inserts, updates, and deletes on the LapTop

Step 4 : Make sure TVU does not delete or update data that the Master will have worked on during the week.

Step 5 : When the TVU returns, run START SLAVE; on the Master to reconnect the Master to the LapTop. All inserts, updates, and deletes that occurred on the LapTop during the week will transmit over to the Master. Run SHOW SLAVE STATUS\G every couple of minutes on the Master and look for Seconds_Behind_Master going to 0. When it does, the data from the LapTop will be sync'd over to the Master.

Step 6 : (OPTIONAL) Run START SLAVE; on the LapTop to bring all the inserts, updates, and deletes the Master did during the week. Run SHOW SLAVE STATUS\G every couple of minutes on the LapTop and look for Seconds_Behind_Master going to 0. When it does, the data from the Master will be sync'd over to the LapTop.

The only real danger is if you delete or update data on the LapTop that still needs to be on the Master. If you forget that, step 5 will make that data change or disappear unintentionally. As long as you work with a new set of data on the LapTop only, there should be no problem.

You should test this between a DevServer and a LapTop you are using for Development only.

UPDATE 2011-07-24 21:42 EDT

Here is another thing you can try:

Step 1 : Setup mysql on the LapTop with no initial data on the laptop and no binary logging

Step 2 : mysqldump the data out of the Master and into the LapTop

Step 3 : Add this to my.ini on the LapTop

[mysqld]
log-bin=mysql-bin

Step 4 : Activate binary logging without a mysql restart on the LapTop

SET GLOBAL SQL_LOG_BIN = 0;

or just restart mysql

Step 5 : Perform inserts, updates, and deletes on the LapTop (Make sure they do not conflict with needed data on the Master)

Step 6 : run this

mysqlbinlog mysql-bin.0* > ThisWeeksChanges.sql

Step 7 : Run this on the Master

mysql> source ThisWeeksChanges.sql

If you have three or more Slaves, I have a nice suggestion: Use one of the Slaves as a Volunteer to be cloned.

Here is a Topology

MAS --+--> SLV1
      |
      +--> SLV2
      |
      +--> SLV0

Say you want to Spawn SLV3. You could use SLV0 as a Clone

• STEP01) Install MySQL Binaries on SLV3 (Same version as all other Slaves)
• STEP02) On SLV0, STOP SLAVE;
• STEP03) On SLV0, service mysql stop
• STEP04) scp -r SLV0:/etc/my.cnf SLV3:/etc/my.cnf
• STEP05) scp -r SLV0:/var/lib/mysql SLV3:/var/lib/mysql
• STEP06) On SLV0, service mysql start
• STEP07) On SLV3, chown -R mysql:mysql /var/lib/mysql
• STEP08) On SLV3, change server_id in /etc/my.cnf to be unique from all other Slaves
• STEP09) On SLV3, service mysql start

That's it.

This is the same paradigm followed by Percona XtraDB Cluster (PXC). When it comes to PXC, introducing a New Slave in PXC is as simple as adding the MasterIP to my.cnf and starting MySQL. All of the above steps are executed internally by PXC using Quorom Selection to choose which Slave becomes the Donor (a.k.a. Volunteer to be Cloned) as well as one of three methods for copying data (xtrabackup, rsync, mysqldump) This copying method is known as SST (State Snapshot Transfer).

If all of the Application-Level Data are stored in InnoDB only, you should look into using PXC. If you have a mix of InnoDB/MyISAM or all MyISAM, the above 9 steps are to be scripted by you.