A Survey of Distributed Query Optimizations

he distributed query optimization is one of the hardest problems in the database area. The great commercial success of database systems is partly due to the development of sophisticated query optimization technology where users pose queries in a declarative way using SQL or OQL and the optimizer of the database system finds a good way (i. e. plan) to execute these queries. The optimizer, for example, determines which indices should be used to execute a query and in which order the operations of a query (e. g. joins, selects, and projects) should be executed. To this end, the optimizer enumerates alternative plans, estimates the cost of every plan using a cost model, and chooses the plan with lowest cost. There has been much research into this field. In this paper, we study the problem of distributed query optimization; we focus on the basic components of the distributed query optimizer, i. e. search space, search strategy, and cost model. A survey of the available work into this field is given. Finally, some future work is highlighted based on some recent work that uses mobile agent technologies