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From "Mathias Herberts" <>
Subject Master/Slave questions
Date Fri, 19 May 2006 07:53:45 GMT
Hi, I am in the process of evaluating ActiveMQ in HA topologies. I am
currently doing some tests with the Master/Slave replication and I
have a few questions:

Can the slave *catch up* if it is started some time after the master?,
i.e. master is started at t0 for the first time, slave is started at
t0+d also for the first time, will the slave be aware of every message
persisted between t0 and t0+d?

If not how can a master and slave be synchronized either at startup or
after a communication failure between the two?

I understand that the master will not answer its clients until the
operation has been replicated to the slave(s), but since the master is
not aware it has slaves until they come up, this whole master/slave
replication is rather incomplete, i.e. the master will happily respond
to its clients if the slave is not currently connecter, which makes
the process rather useless in case of failure since the slave will not
have a coherent view of the master's state.

What would really be nice would be to have the following commands that
could be passed to activemq:

- HOLD, freeze the state of the master
- FLUSH, flush any data needing to persist to persistent storage,
making the persistent storage stable and coherent.

this storage could then be replicated (using rsync for file based
storage or using DB replication for DB based storage) on any number of

- RELEASE, unfreeze the master and resume current operations.

Right now I do not see how to set up a secure DR topology ensuring
coherent states on the slave.

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