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From:Ph.D. Joseph E. Sacco Date:July 9 2004 2:39pm
Subject:node groups
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(0) What are the relationships between the number of replicas,the number
of node groups, and the number of nodes per node group?

(1) Should there be a configuration tag that assigns a db node to a
specific node group?

(2) Are node groups immutable?

It would appear that:

* (number of db nodes) % (number of replicas) = 0
* (number of db nodes) % (number of node groups) = 0
* in a given configuration all node groups must have the same number of
db nodes:
(number of db nodes per node group) = 
			(number of db nodes)/(number of replicas)

Are these relation sips correct? Are there any other constraints?

I have noticed that db nodes are assigned sequentially to node groups.
For example, consider a cluster with two replicas and four db nodes with
node Id's 2->5. The system will create two node groups and assign in
sequence two nodes to each node group:

	node group 1: DB2 + DB3
	node group 2: DB4 + DB5

It is important for an administrator to know that the assignment of db
nodes to node groups is sequential, particularly if the administrator
wishes to distribute each node group across multiple computers. In the
current example, DB2 and DB4 should be configured to execute on one
computer while DB3 and DB5 should be configured to execute on the other.

I guess the answer to my second question depends upon how many DB nodes
and how many replicas are in the cluster. If the number of nodes is not
huge, the cluster configuration task is manageable. Adding appropriate
comments to the config.ini file should suffice.

My third question comes from thinking about cluster maintenance and
cluster extensibility. I have conducted a few [albeit incomplete]
experiments. It would appear at present that changing the cluster
configuration requires rebuilding the cluster from scratch. 

I can easily envision situations where it becomes necessary to add more
db nodes to an existing cluster. How will this be done?

	dump -> reconfigure -> restore  ???

Whether or not this is a big issue, a small issue, or a non-issue comes
down to the amount of time required [cost] to perform the task. The old
mainframe data center operational model where there was a scheduled
eight hour window of downtime each week for maintenance is rapidly
becoming a thing of the past in the 7x24 e-world.


Joseph E. Sacco, Ph.D. <jsacco[at]earthlink[dot]net>

node groupsPh.D. Joseph E. Sacco9 Jul
  • Re: node groupsMichael Dykman14 Jul