View Consistency For Mobile Replication

Replicated systems provide higher availability of data by storing data at locations where the data is more likely to be accessed. The replicated data must be kept consistent, so that when different copies are accessed, they yield the same data. Data can be kept consistent conservatively or optimistically.

Conservative Consistency

Conservative consistency provides a good user model by making replication completely transparent to the user. However it provides low availability of data during network partitions thus negating the availability advantages of replication.

And low availability does not work for the mobile user.

Optimistic Consistency

Optimistically replicated systems provide high availability of data by allowing updates to any available copy of the data. Unfortunately these independant updates can be conflicting. These update conflicts are resolved at some later time. Thus a user may obtain random views of the state of the file during the time between the update and the conflict resolution.

Conservative and optimistic consistency represent two ends of the availability and consistency spectrum:


Consistency for Mobile Applications

Neither conservative nor optimistic consistency provide the consistency requirements for mobile computing. We propose the View Consistency Model that offers enhanced consistency guarantees at a low cost without affecting availability significantly. Read on ...

Here's a postscript version of my masters thesis.


The view consistency work is part of the Traveler Project. at UCLA. Thanx for taking the time to browse through my work. For a better view of things, comments, complaints or to just talk to me ...

Ashvin Goel