Adaptive Web Caching

CS411 Dynamic Web-Based Systems

Flying PigFei Teng/Long Zhao/Pallavi Shinde

Computer Science Department

ADAPTIVE WEB CACHING

Contents

1. Introduction2. Related Research3. Main Findings4. An Ideal Adaptive Web Caching System5. Multicast6. Request Forwarding7. Page Retrieval8. Hierarchy and Scalability9. Auto-configuration of Cache Groups10. Group Creation and Maintenance11. Conclusions12. Future Scope

The World Wide Web has seen an exponential growth in:

• the user population• the total host count • the amount of total traffic volume

Introduction

Popular web pages create ‘hot-spots’ of network load due to the same data transmitted over the same network links repeatedly to different users.

The solution is obviously Caching

ADAPTIVE WEB CACHING

• The solution to data dissemination to a multitude of users is to create a multicast delivery system – i.e. data should be fetched only once and forwarded via a multicast tree to different users

Introduction

• As requests on the web are asynchronous – web multicasting is done via caching

• The challenge in building a caching system is not knowing beforehand which pages the users will be requesting

• This is where an Adaptive Web Caching System comes in...

ADAPTIVE WEB CACHING

Related ResearchADAPTIVE WEB CACHING

The Harvest/SQUID Object Cache is a Web caching infrastructure currently being deployed in the Internet.

All cache servers in the SQUID system are connected in a manually configured hierarchical tree

This project has helped reduce unnecessary network load through caching

Related ResearchADAPTIVE WEB CACHING

However, there are limitations due to manual configuration of such large systems:

• the burden on system administrators to configure the cache hierarchy and to coordinate with each other

• the inevitable human errors

• misunderstanding of issues concerning the overall system performance

• the desire for local optimization

• And the lack of adaptivity to network changes

Main FindingsADAPTIVE WEB CACHING

An Adaptive Web Caching System has the following characteristics

• Auto-configuring

• Routes requests to the nearest cache likely to have the data

• Adaptive to changes in topology, load, user demands, etc.

• An overlapping mesh, with each page having its own cache tree

• Scalable

Ideally the more a page is requested by users, the page would automatically walk down the distribution tree (i.e. it is proportional to the intensity of the requests).

An Ideal Adaptive Web Caching System

This way the most popular pages would be the closest to the end user and more cached copies of these pages would exist.

While pages that have been rarely requested for will either not leave the origin server of be very high up in the distribution tree.

An ‘adaptive’ system will load itself according to the demand

ADAPTIVE WEB CACHING

IP multicast can be used as a basic building block to build this system. The adaptive caching system makes use of both features of IP multicasting:

Multicast

• Multicast page requests to locate nearest cache copy available

• Multicast page responses in order to efficiently disseminate pages with common interests

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Request Forwarding

• Cache servers join more than one multicast group, this way all cache groups heavily overlap each other.

• If there is a cache miss in one group, each cache checks if its other cache groups lie in the direction towards the origin server of the requested page.

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Page Retrieval

• Once a request reaches a group of servers that have requested it, the node holding the page multicasts the response to the group.

• This also loads the neighbouring caches in the same group with the page.

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Hierarchy and Scalability

• On a base of overlapping mesh, each popular page grows its own cache tree.

• Cache pages based on the popularity of the page allows the design of this system to scale well with large user populations.

• Cache tree for each page may grow dynamically, but the cache groups remain relatively stable.

ADAPTIVE WEB CACHING

Auto-configuration of Cache Groups

• Manual configuration does not scale (For ex. SQUID system)

• Manual configuration tend to be error-prune

• Self-configuring capabilities allow cache groups to adapt according to changing conditions in network topology, traffic load, user demand etc.

For the Cache Group infrastructure to be scalable and robust, they need to be self-configuring for the following reasons:

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Group Creation and Maintenance

• regrouping according to the observed group load

• the group cache hit ratio

• the tolerance of group overhead

The basic functionality for cache group managements concerns group creation and maintenance. This includes:

• the change in topology and caches

Group Creation and MaintenanceADAPTIVE WEB CACHING

• An open membership policy for cache groups

• No authentication step required

• Cache consistency and data authentication must be properties that reside in the data

ConclusionsADAPTIVE WEB CACHING

• no manual configuration required, it is auto-configuring

With this Adaptive Web Caching System:

Higher the demand for a page = Page further down the distribution

tree and closer to the end user

ConclusionsADAPTIVE WEB CACHING

Cache trees can automatically build themselves as popular pages are pulled down towards their clients.

With time the trees should also automatically vanish as the pages become a past interest.

• is adaptive to changes in topology, load, user demands, etc.

Future ScopeADAPTIVE WEB CACHING

• incremental deployment into the current unicast caching infrastructure of dynamic mechanisms for forwarding requests to neighbouring caches

• incremental deployment of a multicast-based cache architecture into the existing architecture of unicast communications between clients, web caches, and servers

Collaboration with the Harvest/SQUID Caching team to explore transition strategies to convert the current manually configured caching infrastructure into an auto-configured adaptive caching system.

Thank you for listening!ADAPTIVE WEB CACHING

Questions?