Implementing a Distributed Peer to Peer File Sharing System ... - Umbc

CHEWBACCA Baker, Fink, Trimm, Whisman
filled in, the joining node must update every node that should have it in their finger
tables. Initially, M “update your finger table with me” messages are sent out to the
existing nodes. Since the recipients of this message must first be found, the number of
messages is M*Log(N). Additionally, each node that receives one of these messages
may pass it to their predecessor if they, themselves, updated their table. If the nodes are
perfectly distributed around the virtual ring, then one node, at most, is updated with each
of these messages. Therefore, the number of messages for join is M*Log(N) +
M*Log(N) or O(M*Log(N)). The correct estimate with varying M’s is shown in Fig. 3.
The leave operation performs in a similar manner to the join operation except that it
doesn’t fill in its own finger table. However the “update others” method is very similar
to the joins with the modification that you are telling other nodes to replace entries of the
leaving node with its successor. Therefore, the number of messages for leave is
M*Log(N). This estimate with varying M’s is shown in Fig. 4.
The find operation performs as specified by the Chord Paper. This is intuitively obvious
because the Chord finger table implements a distributed binary search. For every hop
that a find message takes, it roughly halves its distance to the searched for slot. The
metrics for the find operation are shown in Fig. 5.
5.2.3 Results of Improvements
Standard Deviation of Inter-node
Distances
60000
50000
40000
30000
20000
10000
Unbalanced vs. Balanced Joins, M=20
0
0 10 20 30 40 50 60 70
Nodes
Unbalanced Join
Balanced Join
Figure 6. The number of messages required using balanced-join compared with those
required using join
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