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From "Edelstein, Lawrence" <>
Subject improve master/slave topology
Date Wed, 08 Mar 2006 18:50:31 GMT
(Sorry not to reply to Ning Li's message, but I just subscribed to the list, and don't know
how to reply to it without it being in my inbox.)


This is just my quick naïve stab at how resynching might work:


-          When the master is notified of a slave, it makes a persistent note of the slave's
identity (presumably URI).

-          When the master goes down, the slave begins operating as it does now.  It also
starts a new transacted message queue (the "resynch queue") for all the messages and acknowledgements
it's going to process while it is in the hot seat.

-          When the master comes back up:

o        Before it begins responding to messages, it looks for its persistent note, and finds
the slave.  

o        It connects to the slave and tells it that their places are reversed.  The Servant
Has Become The Master.  Biblical scholars and Police fans laugh.  (FROM NOW ON, I'LL REFER
TO THE BROKERS USING THEIR NEW ROLES.)  The new slave will not process messages from anybody
but the new master.

o        The new slave begins consuming resynch messages from the queue, as well as those
new messages that come from its new master via the good ole' master-slave protocol, processing
each in the same way.  Er, somehow.


If I correctly understand how clients work, then the next step should not require any notification
to the clients:


-          The slave and master agree to swap places.  The swap takes place atomically with
respect to all of the ongoing synchronization processing between them.  (NOW I'LL REFER TO


At this point the slave stops processing requests, and the master starts; clients should be
able to failover just as they do now.


If someone wants to point me the way to relevant code, I'll check it out.  Perhaps I've really
oversimplified things...if so, please tell me where.


Larry Edelstein

Revere Data

San Francisco, CA

--- on Mon March 6, Ning Li wrote: ---
Maybe a broker-broker synchronization protocol is the ultimate solution, just we are not sure
how to get there. Any recommendation or suggestions?




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