From: Marcel Ruff [SMTP:mr at marcelruff.info]
Sent: Friday, April 18, 2003 1:03 PM
To: xmlblaster at server.xmlblaster.org
Subject: Re: [xmlblaster] Clustering or simply server to server
Madere, Colin wrote:
I'm getting a little lost in the documentation, so I decided to post my
I'm interested in setting up multiple servers which pass all or a
subset of message to each other. I guess I would set up the "Domain"idea
as I saw in the docs, however, the choice of "masters of topics" will becertain
arbitrary since there won't be an application level requirement of a
location being the master of most of the topics. A few will have that
property, but most will not.
In that same vein, if I arbitrarily choose a master for a topic (or
of topics) and that server is disconnected from the rest, won't this meanof
that messages published to non-masters will not be propogated to others
since only the master propogates topic publishes to the "slaves"? I kind
want to avoid that... so is that one of the clustering features that hasnot
yet been implemented?
You got the point.
The current clustering support was a first shot, it supports exactly
what i needed in a commercial project.
Having mirrored cluster nodes (for fail over) is not implemented yet.
The current clustering is a good base to add such features, but
it still takes time to do and document and test it, it involves:
o Only messages of stratum level 0 are mirrored
o A cluster setup may have any number of mirror nodes
o Changing mirror nodes to hot standby and adding mirror
nodes in hot operation needs to be supported (administrative control).
o If a cluster collective breaks into pieces (no heartbeat) we need
a semaphore (depending on the size of the sub collectives) to
decide which sub collective takes over the leadership
o The session informations need to be mirrored as well
(time to live, subscribes, callback queue states for persistent
o The client library needs to be extended to change to other mirror
nodes on failure (this is reused in the cluster nodes themselves
when connecting to other nodes)
As soon as somebody has some Euros/Kroner left in his commercial
project and needs it we could add these features :-)
Follow-up questions, it seems, would be:
1) Is clustering implemented in a functionally complete way for sharing
topics amonst multiple instances in a non-load balancing structure?
As mentioned, no mirroring is implemented.
Probably this can somehow partly be simulated with the current
there are examples to play with (just start the servers in different
2) Is anyone successfully using the clustering setup that is currently
available in xmlBlaster?
I do, it is a commercial clustering setup with a master and many slaves
for realtime radar/GPS data of ships.
Thanks in advance for you input.