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From Peter Dijkshoorn <>
Subject architectural understanding of write operation node flow
Date Mon, 23 Jan 2012 15:47:11 GMT

Hi guys,

I got an architectural question about how a write operation flows
through the nodes.

As far as I understand now, a client sends its write operation to
whatever node it was set to use and if that node does not contain the
data for this key K, then this node forwards the operation to the first
node given by the hash function. This first node having key K then
contacts the replication nodes depending on the selected consistency level.

This means that in the unlucky event you always have a network call
sequence depth of 2 (consistency level one), or 3 (assumed that the
replication nodes are contacted in parallel)

This is more than I expected, so I am not sure whether this is correct?
can someone help me out?

At first I thought that the receiver was the coordinator, and thus doing
all further calls in parallel, the depth as described above would always
be 2. But I just discovered that I was wrong and that it should be
something like above.

Another possibility would be that the client learnt the layout of the
cluster at connection time and thereby tries per request to contact the
coordinator directly, but I never read or see something like this happening.

Remembering the picture of Dean about network and hard disk latencies,
is this 3-sequential-network-call still faster?

Thanks for any thoughts :)


Peter Dijkshoorn
Adyen - Payments Made Easy

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