Adaptive Load Sharing for Clustered Digital Library Servers Song, yong-joo System Software Lab, EECS, KAIST 9. 13, 2000.

Adaptive Load Sharing for Clustered Digital Library Servers

Song, yong-joo

System Software Lab, EECS, KAIST9. 13, 2000

Contents Introduction Previous Work

Clustered ADL server design Load sharing strategy Policy for node selection & load collection

Experiment Conclusion & Critique

3

Introduction Alexandria digital library

Geographically-referenced materials Map, satellite image, digitized aerial photograph

Large data Require extensive processing

Goal : minimize response time

4

Introduction(cont’d)

Basic ADL Clustered ADL

5

6

Previous Work Clustered Web server design

DNS round-robin rotation Problem : load imbalance

SWEB Redirecting request by dynamic system load prediction of response time

7

SWEB DNS round-robin rotation Redirect request to minimum expected

response time server

CPU, I/O load monitoring

prediction of DB searching time load information update

overhead

8

Load Sharing strategy Class of request

Text & image ( CPU & I/O usage small ) DB search ( CPU & I/O usage maybe large ) Image processing ( predictable )

Relative Server-site Response Cost Availability relative to the unloaded base node

redirection threshold value

atioDiskAvailRdthDiskBandwindwidthBaseDiskBa

IdleRatioCPUSpeededBaseCPUSpeRSRC

)1(

9

Policy for load collection Broadcast – redundant info, load explosion Random poll – synchronization overhead

Proposed Random multicast

A hybrid approach Random multicast + Random poll

)1)(1()1( atioDiskAvailRIdleRatio

10

Experiment Server

6 of 147Mhz 2 of dual 167Mhz

Multi-node performance Comparison of load collection policies Effectiveness of RSRC func.

11

Conclusion Study adaptive load balancing strategy

Consider both I/O & CPU load factor On non-uniform cluster Hybrid node selection & collection policy

12

Critique SWEB does not consider non-uniform

cluster? RSRC correctness Parameter, threshold value decision Multicast overhead

How about Broadcast & selective catch