Abstract: A system and method is provided for distributed relational databases for parallel sorting of a relation wherein the relation is a set of tuples to be sorted on multiple sort sites which completely decouples the return phase from the sort phase in order to eliminate the merge phase. The method involves selecting one coordinator site from any of the available logical sites, then generating and sorting a local sample on each of the available storage sites before sending the local random sample from each storage site to the designated coordinator site wherein the local random samples are merged to provide a single global sample. The coordinator site determines the global interval key values based on the global sample. The interval key values being determined such that each interval fits in a single sort site's main memory, wherein the tuples between two interval key values define the interval.

Abstract: A method for choosing join selectivities in a query optimizer in a relational database management system is disclosed which facilitates the estimation of join result sizes by a query optimizer in a relational database system, wherein a new relation R is to be joined with an intermediate relation I, and wherein the selectivity values for each eligible join predicate are known. The method has the steps of determining the equivalence classes for a plurality of join attributes and then computing for each relation an estimate of the cardinality and the number of distinct values in each attribute after all the local predicates have been included. These are used in further computation of join selectivities and join result sizes. The join predicates must then be processed by correctly choosing the join selectivities. The join result sizes can then be correctly calculated.

Abstract: A method for choosing join selectivities in a query optimizer in a relational database management system is disclosed which facilitates the estimation of join result sizes by a query optimizer in a relational database system, wherein a new relation R is to be joined with an intermediate relation I, and wherein the selectivity values for each eligible join predicate are known. The method has the steps of determining the equivalence classes for a plurality of join attributes and then computing for each relation an estimate of the cardinality and the number of distinct values in each attribute after all the local predicates have been included. These are used in further computation of join selectivities and join result sizes. The join predicates must then be processed by correctly choosing the join selectivities. The join result sizes can then be correctly calculated.

Abstract: A join optimization method is provided for use with a data processor for optimizing the processing of a query for retrieval of data from a relational computer database. The database is organized by relations and data is retrieved by preforming join operations on the relations. The join operations are optimized by randomly selecting an initial order for the join operations, assigning optimal join methods based on the initial order, finding an optimal order based on the assigned methods and repeating a polynomial number of times. The Krishanmurthy, Boral and Zaniolo (KBZ) Algorithm is used to determine a join optimization sequence and further refinement is provided by determining costs for alternate join order sequences using alternate join methods.