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From Philip Stanhope <pstanh...@wimba.com>
Subject Seeds, autobootstrap nodes, and replication factor
Date Fri, 04 Jun 2010 17:36:22 GMT

Here's the scenario: would like R = N where N is the number of nodes. Let's say 8.

1. Create first node, modify storage-conf.xml and change the <Seed/> to be the ip of
the node. Change replication factor to 8 for CF of interest. Start the puppy up.

2. Create 2nd node, modify storage-confg.xml and change <AutoBootstrap/> to true and
let it know the first seed. Ensure replication factor is 8 for the CF of interest. Start the
puppy up.

3. Create 3rd node. 

Q1: Should the node1 and node2 be listed as seeds? Or only node1?

4. Create 4th node. Same question as before.  

Q2: Same question as before ... should the list of seeds grow as the cluster grows? Alternative
phrasing ... what is the relationship between Seed and AutoBootstrap, i.e. can a Seed node
in fact be a node that was autobootstrapped? Is this considered best practice?

At this point we've got 4 nodes in the cluster ... I've gotten this far with no problems,
loaded with tons of data and compared performance with various replication factors. Seeing
faster reads from any particular node (as expected) when the ReplicationFactor is equal to
the number of nodes in the cluster. Have compared lots of single update/creates as well as
batch_mutate (which is very fast for bootstrapping the CFs -- highly recommended).

And also seeing varying performance on reads (fast, and as expected) when ReplicationFactor
< N. 

Q3: What, if any issue, is there when R > N?	

This is the situation as you're bringing up nodes in the cluster. And when you take down a
node (intentionally or as a failure).

I know one consideration is that if R >= N ... and CF data grows ever bigger ... there
will be a hit as the node is created.

Q4: If you know that you're never going to have more than 40 (MaxExpectedClusterNodes) in
your cluster ... is it safe to set R >= MaxExpectedClusterNodes? 

Q5: If you set R = MaxExpectedClusterNodes ... and you end up servicing a node .... and bringing
up an alternate node in its place ... thus having R = N at all times ... and then you bring
up the N+1 node ... will it start to receive the data that it missed while it was down?

I tried asking similar questions a few weeks ago on the IRC ... but have much more experience
now and am trying to figure out best practices and document for my ops team.

-phil
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