Dean Daniels

Query Processing in R

This chapter describes how statements in the SQL language are processed by the R* distributed relational database management system. R* is an experimental adaptation of System R to the distributed environment. The R* prototype is currently operational on multiple machines running the MVS operating system, and is undergoing evaluation. The R* system is a confederation of autonomous, locally-administered databases that may be geographically dispersed, yet which appear to the user as a single database. Naming conventions permit R* to access tables at remote sites without resorting to a centralized or replicated catalog, and without the user having to specify either the current location of or the communication commands required to access that table. SQL data definition statements affecting remote sites are interpreted through a distributed recursive call mechanism. Tables may be moved physically to other databases without affecting existing SQL statements. SQL data manipulation statements are compiled at each site having a table referenced in the statement, coordinated by the site at which the statement originated. As part of compilation, the distributed optimization process chooses the best place and the best way to access tables and join them together. Optimization uses dynamic programming and careful pruning to minimize total estimated execution cost at all sites, which is a linear combination of CPU, I/O, and communications (both per-message and per-byte) costs.

Site autonomy issues in R∗: A distributed database management system☆

Abstract A distributed database management system (DDBMS) must simplify the users task of defining applications which manipulate shared data stored at multiple computing sites. To this end, the DDBMS must support transparent access to remote data. That is, any operation allowed on local data should also be possible on remote data. At the same time, because different computing sites are controlled by different individuals or organizations, the DDBMS must preserve each sites autonomy over its own data. This paper discusses some of the issues raised in the implementation of a DDBMS by the requirements of site autonomy. The issues will be discussed from the perspective of the R ∗ research project at IBMs San Jose Research Lab.