GIA: Making Gnutella-like P2P Systems Scalable

Yatin Chawathe

Sylvia Ratnasamy, Scott Shenker, Nick Lanham,

Lee Breslau

Parts of it has been adopted from the authors’ original presentation

The Peer-to-peer Phenomenon

• Internet-scale distributed system– Distributed file-sharing applications

e.g., Napster, Gnutella, KaZaA

• File sharing is the dominant P2P app

• Mass-market– Mostly music, some video, software

The Problem

• Large scale system: millions of users– Wide range of heterogeneity– Large transient user population (in a system with

100,000 nodes, 1600 nodes join and leave per minute)

• Existing search solutions cannot scale– Flooding-based solutions limit capacity– Distributed Hash Tables (DHTs) not

necessarily appropriate

A Solution: GIA

• Scalable Gnutella-like P2P system

• Design principles:– Explicitly account for node heterogeneity– Query load proportional to node capacity

• Results:– GIA outperforms Gnutella by 3–5 orders of

magnitude

Outline

• Existing approaches

• GIA: Scalable Gnutella

• Results: Simulations & Experiments

• Conclusion

Gnutella

• Distributed search and download• Unstructured: ad-hoc topology

– Peers connect to random nodes– Supports keyword–based

search• Random search

– Flood queries across network• Scaling problems

– As network grows, search overhead increases

P1

P2

P4

P3

who has“madonna”

P 4 has “

madonna-

american-lif

e.mp3”

P5P6

P2 has “madonna-ray-of light.mp3”

Distributed Hash Tables (DHTs)

• Structured solution– Given the exact filename, find its location

• Can DHTs do file sharing? – Yes, but with lots of extra work needed for

keyword searching

• Do we need DHTs?• Not necessarily: Great at finding rare files, but most

queries are for popular files

• Poor handling of churn – why?

Other Solutions

• Supernodes [KaZaA]

– Classify nodes as low- or high-capacity

– Only pushes the problem to a bigger scale

• Random Walks [Lv et al]

– Forwarding is blind

– Queries can get stuck in overloaded nodes

• Biased Random Walks [Adamic et al]

– Right idea, but exacerbates overloaded-node problem

Outline

• Existing approaches

• GIA: Scalable Gnutella

• Results: Simulations & Experiments

• Conclusion

GIA: High-level view

• Unstructured, but take node capacity into account– High-capacity nodes have room for more

queries: so, send most queries to them

• Will work only if high-capacity nodes:– Have correspondingly more answers, and– Are easily reachable from other nodes

• Make high-capacity nodes easily reachable– Dynamic topology adaptation converts them into high-

degree nodes

• Make high-capacity nodes have more answers– One-hop replication

• Search efficiently– Biased random walks

• Prevent overloaded nodes– Active flow control

GIA Design

Query

Dynamic Topology Adaptation

• Make high-capacity nodes have high degree (i.e., more neighbors), and keep low capacity nodes within short reach from them.

• Per-node level of satisfaction, S:– 0 no neighbors, 1 enough neighbors

Satisfaction S is a function of: ● Node’s capacity ● Neighbors’ capacities

● Neighbors’ degrees

When S << 1, look for neighbors aggressively

Dynamic Topology Adaptation

Each GIA node maintains a host cache containing a list of other GIA nodes. The host cache is populated using a variety of methods (like contacting well-known web-based hosts, and exchanging host information using PING-PONG messages.

A node X with S < 1 randomly picks a node Y from its host cache, and examines if it can be added as a neighbor.

Topology adaptation steps

Life of Node X: it picks node Y from its host cache

Case 1 {Y can be added as a new neighbor}(Let Ci represent capacity of node i)if num nbrsX + 1 < max nbrs then we have roomACCEPT Y ; return

Case 2 {Node X decides if to replace an existing neighbor in favor of Y}subset := i U i nbrsX : Ci ≤ CY

if no such neighbors exist then REJECT Y ; returnelse candidate Z := highest-degree neighbor from subset

If Y has higher capacity than Zor (num nbrsZ > num nbrsY + H) {Y has fewer nbrs}

then DROP Z; ACCEPT Yelse REJECT Y{Do not drop poorly connected nodes in favor of well-connected ones}

Active Flow Control

• Accept queries based on capacity

– Actively allocation “tokens” to neighbors

– Send query to neighbor only if we have received token from it

• Incentives for advertising true capacity

– High capacity neighbors get more tokens to send outgoing queries

– Allocate tokens with start-time fair queuing. Nodes not using their tokens are marked inactive and this capacity id redistributed among its neighbors.

Practical Considerations

• Query resilience: node death– Periodic keep-alive messages

– Query responses are implicit keep-alive messages

• Determining node capacity– Function of bandwidth and storage

• Each query is assigned a unique GUID by its originator. – This helps with reverse-path forwarding of responses.

Returning queries are forwarded to a different neighbor, so that they don’t traverse the same path twice

Outline

• Existing approaches

• GIA: Scalable Gnutella

• Results: Simulations & Experiments

• Conclusion

Simulation Results

• Compare four systems– FLOOD: TTL-scoped, random topologies– RWRT: Random walks, random topologies– SUPER: Supernode-based search– GIA: search using GIA protocol suite

• Metric:– Collapse point: aggregate throughput that the

system can sustain (per node query rate beyondwhich the success rate drops below 90%)

Questions

• What is the relative performance of the four algorithms?

• Which of the GIA components matters the most?

• How does the system behave in the face of transient nodes?

System Performance

0.00001

0.001

0.1

10

1000

0.01 0.1 1Replication Rate (percentage)

Collapse Point (qps/node)

GIA: N=10,000

SUPER: N=10,000

RWRT: N=10,000

FLOOD: N=10,000

GIA outperforms SUPER, RWRT & FLOOD by many GIA outperforms SUPER, RWRT & FLOOD by many orders of magnitude in terms of aggregate query loadorders of magnitude in terms of aggregate query load

% % %

population of the object

Factor Analysis

Algorithm Collapse point

RWRT 0.0005

RWRT+OHR 0.005RWRT+BIAS 0.0015

RWRT+TADAPT 0.001RWRT+FLWCTL 0.0006

Algorithm Collapse point

GIA 7

GIA – OHR 0.004GIA – BIAS 6

GIA – TADAPT 0.2

GIA – FLWCTL 2

Topologyadaptation Flow control

No single component is useful by itself; the combinationof them all is what makes GIA scalable

Transient Behavior

0.001

0.01

0.1

1

10

100

1000

10 100 1000 10000Per-node max-lifetime (seconds)

Collapse point (qps/node)

replication rate = 1.0%

replication rate = 0.5%

replication rate = 0.1%

Static SUPER

Static RWRT (1% repl)

Even under heavy churn, GIA outperforms the otheralgorithms by many orders of magnitude

Deployment

• Prototype client implementation using C++

• Deployed on PlanetLab:– 100 machines spread across 4 continents

• Measured the progress of topology adaptation…

Progress of Topology Adaptation

0

10

20

30

40

50

0 20 40 60 80 100Time (seconds)

Number of neighbors

C=1xC=10xC=100xC=1000x

Nodes quickly discover each other and soon reach their target “satisfaction level”

Outline

• Existing approaches

• GIA: Scalable Gnutella

• Results: Simulations & Experiments

• Conclusion

Summary

• GIA: scalable Gnutella– 3–5 orders of magnitude improvement in

system capacity

• Unstructured approach is good enough!– DHTs may be overkill– Incremental changes to deployed systems

• Status: Prototype implementation deployed on PlanetLab