Transcript Elders know best: Lifespan-based ideas in P2P systems

Elders know best
Lifespan-based ideas in P2P systems
Yi Qiao & Fabián E. Bustamante
Department of Computer Science
Northwestern University
{yqiao,fabianb}cs.northwestern.edu
www.aqualab.cs.northwestern.edu
P2P systems & transient populations
P2P purest form – all peers are equal
–
–
Simple protocols
Clash with reality → loss of most appealing attributes
Highly transient population
– As undesirable as unavoidable
→ Maintenance-related messages, plus
→ Degree of replication, effectiveness of caches, spread of
queries, overall system scalability, …
Same for other large-scale distributed systems
Dept. of Computer Science
Northwestern University
2
Peer lifespan distribution
Active probing in Gnutella > 7
days
500,000 peers, ~1 million
peers’ lifespans
Fits a Pareto distribution well
(R2 ~ 0.99)
In this context …
Peer’s expected remaining
lifetime proportional to its
current age
Dept. of Computer Science
Northwestern University
3
Lifespan protocols & strategies
Lifespan-based protocols
– Network stability – connection breakdown & rejection,
number of connections per peer, ….
– Effects on the application – query hits & response time
Lifespan-based strategies
– query distribution, caching, replication
Experimental setup
–
–
–
–
Trace-driven simulation
4/20 collected traces, period 510,000 sec., ~150,000 peers
~3-4,000 peers under stable conditions
Cold start, warm-up ~80,000 sec. excluded
Dept. of Computer Science
Northwestern University
4
LSPAN-based protocols
Lower connection breakdowns
~30-42% reduction!
With low rejection rates –
LSPAN-3 ~ 1 every 17.58 hrs!
Random-Walk & Neighbor
Caching
Same hit rate & query response
time with 5 instead of 16
random walkers!
Gnutella
KaZaa
LSPAN-based
Dept. of Computer Science
Northwestern University
5
Elders know best – new strategies
Query distribution - LSPAN-biased random walk
Replication - Region-based instead path-replication
Higher query satisfaction
Finding “needles”
Dept. of Computer Science
Northwestern University
6
Conclusions and future work
To deal with transient populations, pay
attention to your seniors
– More stable P2P systems
– Faster queries replies, more query hits, …
– More scalable P2P systems
Soon
– More results
– Wide-area evaluation on PlanetLab
– Lifespan and DHTs?
Dept. of Computer Science
Northwestern University
7