wcw2004 overhaul

8/9/2019 Wcw2004 Overhaul

1/25

Overhaul: Extending HTTP to

Combat Flash CrowdsJay A. Patel & Indranil Gupta

Distributed Protocols Research Group

Department of Computer Science

University of Illinois at Urbana-Champaign (UIUC)

Urbana, Illinois, USA


2/25


3/25

Distributed Protocols Research Group, Department of Computer Science, University of I ll inois at Urbana-Champaign 3

Example: MSNBC

MSNBC home pageDecember 14, 2003


4/25


Motivation Problem

Unpredictable, yet frequent

Brief period of time

Thousand-fold increase in traffic

Two nave solutions

Overly insure on resources Shut down web site


5/25


Current Solutions Architectural Changes

SEDA

Capriccio ESI

Protocol Modifications

DHTTP

Web Booster

Cooperative Sharing

Squirrel

Kache Backslash

BitTorrent


6/25


HTTP: RegularInteraction

Client Server

GET RequestResponse

DocumentHeader


7/25


Overhaul: Overview Protocol change

HTTP extension, no modification 5 new tags added, 1 slightly modified

Backwards compatible Key concept: chunking

Characteristic of the web applied to individual documents

m chunks per document

P2P distribution framework Voluntary

Ad hoc, not DHT based

Key benefit:parallel resource discovery


8/25


Overhaul: Design

Client

Server

Client

Client

Client#1

#2

#4

#3

HTTP Request

with Overhaul support tag

Chunked Response

with Overhaul headers

Peers exchange chunks

to fetch the complete document

Ad hoc peer network


9/25


Details: Client/ServerInteraction Initial request by client

Supports: Overhaul $port $speed

Response by server in Overhaul mode

ith chunk transmitted in sequential order

Signatures of otherm-1 chunks for verification

Initial Overhaul network membership list n most-recent Overhaul clients

List maintained at server (updated with every request)


10/25

Distributed Protocols Research Group, Department of Computer Science, University of Ill inois at Urbana-Champaign 10

Details: Peer Clients Interaction Clients contact other peer members

To fetch remaining chunks

To discover new peers

Aggregate membership list by swapping information

1-hop random walk discovery process

Resource discovery

Lookup documents on a busy Overhaul server

Contact peers randomly on membership list

INFO $host.tld


11/25


Implementation Server

Apache/2.0 HTTP server

Module:mod_overhaul

Client

Java HTTP Proxy

Cross platform Universal client support


12/25


Testing Methodology: Server Server machine

2.5 GHz AMD Athlon XP+

1 GB RAM Client machine

650 MHz Pentium III

320 MB RAM

Same network equipment

25 concurrent fetches

ApacheBench utility


13/25


Results: Chunking (Fixed Size)Document: 10 KB

Concurrency: 25

Regular HTTP

512-byte chunks

2048-byte chunks

Overhaul mode requires the server to send only a single chunk


14/25


Results: Chunking (Maximum Count)

Regular HTTP

6 chunks

12 chunks

24 chunks

Document: 50 KB

Concurrency: 25


15/25


Results: Overhaul vs. Regular

Regular HTTP

6 chunks

12 chunks

Concurrency: 25

Minimum chunksize: 512-bytes


16/25


Testing Methodology: Client Cluster of workstations

25 homogenous PCs

2.8 GHz Intel Pentium 4

1 GB RAM

Same network equipment

Two experiments

Concurrent: single document

Staggered: multiple documents


17/25


Results: Single Document Large document: 50

KB (12 chunks)

Server condition: 150-250 concurrent fetches

+ competition

Overhaul requests:

concurrently only using 24

Overhaul-aware clients

Regular

requests

Overhaul

mode

Fastest 1 sec 6 secs

Slowest 32 secs 9 secs

Average 9 secs 7 secs

Server bandwidth usage in Overhaul mode: 1/12th of regular requests


18/25


Results: Multiple Documents 8 documents: 110 KB total

(12 chunks)

Server condition: 150-250

concurrent fetches +

competition

Overhaul requests staggered

1st stage: 12 concurrent

fetches, fetch all documents 2nd stage: 12 concurrent

fetches, fetch index document

only

Regular

requests

Overhaul

mode

Fastest 1 sec 14 secs

Slowest 28 secs

Average 23 secs* 18 secs

Server bandwidth usage in Overhaul mode : 1/18th of regular requests

* indicates completed requests


19/25


Limitations Both client and server must be Overhaul

aware

Requires critical mass to be maintained toremain effective

n clients > m chunks

More responsibilities for the client Possible security implications


20/25


Conclusion Saves resources

Bandwidth

The bigger the crowd, the lower the per capita usage Response time

Faster turnaround for both server and client

Getting wide spread acceptance

Marginal cost Protocol extension requires industry and

standards push


21/25


22/25


23/25


Heterogeneous Networks Problem

Connections are

heterogeneous

Solutions

Clustering of clients

Super nodes

Client

Client

Client

Client


24/25


Document Selection Only a partial set of

documents are affected

by a flash crowd Must implement

selective Overhaul

mode

Automatic selection Active monitoring

Server

Large collection of documents

reside on the server

Documents fetched

by a flash crowd


25/25


Dynamic Documents Flash crowds especially frequent during big

events and news

Characteristic: rapidly, changing data

Solutions

Time stamping

Expiration of chunks Inter-network refresh from peers