[chord] Number of nodes in a Chord ring?

[Emil Sit]

On Sun, 14 January 2007 at 11:49 (+0900), Hai Dao Le wrote:
> How to know the exact number of nodes in a Chord ring? I am running
> Chord in my slice which includes all nodes in Planetlab. If I use
> "devel/vis", I see the number is about 250. If I use "devel/walk", the

This number seems most likely to be correct --- vis actually keeps
in memory a list of all the nodes and does not see duplicates; it also
keeps any node that you are able to reach from the local node.

> number of nodes is different for each node I point to (some node reports
> 75, another: 190, another: 315, ...). Which method is more correct? Is
> there another way?

'walk' terminates when it sees the starting node in the walk.  If
its predecessor is unable to reach it due to a transient network
failure, it may skip the starting node and loop around the ring
again.  You might try piping the output of walk through uniq
(e.g. walk -j ... > nodes; cut -d' ' -f1-4 nodes | uniq | wc -l)
for comparison.

-- 
Emil Sit / MIT CSAIL PDOS / http://pdos.csail.mit.edu/chord/