ABSTRACT: In this paper we present a new algorithm for retrieving and updating data from a distributed relational data base. Within such. a data base, any number of relations can be distributed over ' any number of sites. Moreover, a user supplied distribution criteria can optionally be used to specify what site a tuple belongs to. The algorithm is an efficient way to process any query by f'breaking'l the qual-ification into separate "pieces " using a few simple heuristics. The cost cri-teria considered are minimum response time and minimum communications traffic. In addition, the algorithm can optimize separately for two models of a communi-cation network representing respectively ARPANET and ETHERNET like networks. This algorithm is being implemented as part of the INGRES data base system.

This paper presents the concurrency control strategy of SDD-1. SDD-1, a System for Distributed Databases, is a prototype distributed database system being developed by Computer Corporation of America. In SDD-1, portions of data distributed throughout a network may be replicated at multiple sites. The SDD-1 concurrency control guarantees database consistency in the face of such distribution and replication. This paper is one of a series of companion papers on SDD-1[4,10,12,21].

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