MySQL Bugs: #11189: Allowing second mysqld slave process to start will corrupt slave NDB database

Bug #11189	Allowing second mysqld slave process to start will corrupt slave NDB database
Submitted:	9 Jun 2005 2:40	Modified:	13 Jun 2005 18:00
Reporter:	Jonathan Miller	Email Updates:
Status:	Won't fix	Impact on me:	None
Category:	MySQL Cluster: Cluster (NDB) storage engine	Severity:	S4 (Feature request)
Version:	5.1.0-wl2325-wl1354-new	OS:	Linux (Linux)
Assigned to:	Assigned Account	CPU Architecture:	Any

Description:
Two cluster setup, 1st is a master cluster, 2nd is a slave cluster. Each cluster has two mysqld processes. 
Master:
1) Mysqld = A
2) Mysqld = A1

Slave:
1) Mysqld = B
2) Mysqld = B1

Setup and start the bank test for two banks (BANK and BANK2). start A,  A1 and B pulling from A (A->B). All three (A, A1 & B) are in sync. Allow it to run for a while. Then start B1 pulling for A1. B will some time laster error out with:
 Last_Errno: 4350
 Last_Error: Error in Delete_rows event: commit of row events failed
 
After B1 catches up, stop the bank tests. Dump both the master and slave. Compare the two dumps. Some data is in the master but not the slave, and some data is in the slave, but not the master.

How to repeat:
see above

Suggested fix:
Second slave should fail to start (be rejected by the cluster) if a mysqld slave is already updating the slave cluster.

Perhaps if we add the connect string to apply_status, and check that our server id and connectstring match?

This way, you can still change your connect string (by UPDATE) if you change your cluster setup, but this problem will be avoided.

That should, of course, read something like:

check that nobody else is using that connect string.

As it is now it is up to the application programmer to control how he/she want's multiple replication channels to operate on the slave cluster, _and_ take case as not to create conflicts between them  We do not currently supply any mechanisms for "conflict resolution" and or "detection of possible such".

Such functionality is planned for future releases

This bug is not scheduled to be fixed at this time.