Resource Sharing Through Query Process Migration

In this paper we focus on systems whose goal is the distribution or exchange of resources such as software packages, scientific data, or multimedia files. To accomplish this goal efficiently, distributed systems find and retrieve resources using combinations of techniques such as brokering, proxying, caching, publish/subscribe, advertising, chaining, referral, recruiting, etc. The resulting architectures are complex and scale with difficulty. We propose two ideas that combine to make such systems much more scalable. One is to encapsulate queries into processes and to use process migration as the basic primitive for cooperation between sites. With this, a generic installer can run at each site, implementing any and all of the techniques mentioned above. The other idea is to describe resource access as "delayed" queries embedded in metadata. Standard distributed database techniques can be applied to the metadata with the additional side-effect of spawning appropriate query processes. We describe a distributed query language that can be obtained by adding our process manipulation primitives to any query language. We discuss installation strategies and we present an algorithm for the site-generic installer on which such a language is based. We also show how to apply query rewriting techniques that allow the installer to perform optimizations. Moreover, we give algorithms that insure that the global amount of installation associated with a given resource retrieval task is bounded.