Optimising the distributed execution of join queries in polynomial time

It is proposed that an optimal strategy for executing a join query in a distributed database system may be computed in a time which is bounded by a polynomial function of the number of relations and the size parameters of the network. The solution so unveiled considers both the transmission costs and the processing costs incurred in delivering the required result to the user that issued the query. The query specifies that several relational tables are to be coalesced and presented to the appropriate user. Undertaking this task demands the utilisation of limited system resources, so that a strategy for fulfilling the request that imposes minimal cost to the system should be devised. Both the processor sites, and the communications links that interconnect them, are utilised; an optimal strategy is one that minimises a weighted sum of processing and data transmission costs. An integer linear programming model of this problem was originally proposed in [1]; however, no suggestion was given as to how this model might be efficiently solved. By extending the earlier analysis, the recursive nature of the join computation is revealed. Further investigations then produce a modified relationship amenable to algorithmic solution; the resultant procedure has polynomial time and space requirements.