Traditional leases mechanisms for Web-cache consistency employ a single reliable origin server and multiple leaseholders. When a document is updated, the origin sends the update to all leaseholders and caches remain up-to-date. Important issues under this approach are how to reduce the number of messages between the origin and leaseholders, and how to reduce the state that the origin needs to maintain.
We propose to use leases in an a decentralized hosting environment where the origin is a decentralized group of (unreliable) servers. In this environment, reducing origin message and state overhead is not the most important concern, as these are distributed over a large number of servers. The main issue in a decentralized environment is how to deal with origin failures. Leaseholder messaging overhead is also an issue, as each leasholder needs to communicate with multiple origins in order to tolerate failures.
This project involves implementation of a proposed decentralized leases scheme in the context of a collaborative hosting system for Wikipedia, which includes specific subscription, notification and maintenance protocols, as well as lease-renewal strategies.
Prerequisites
Hands-on experience in network programming is required.
References