Query execution scheduling in parallel object-oriented databases

Complex object-oriented queries generally consist of path expressions and e xplicit join operations. Since explicit join operations have been acknowled ged as the most expensive operations, query executions normally start from the path expressions, Each path expression may form a sub-query. There are two existing strategies to sub-queries processing: 'serial' and 'parallel' execution scheduling strategies. Serial sub-queries execution corresponds t o an execution of the sub-queries one-by-one, whereas parallel sub-queries execution corresponds to simultaneous execution of the sub-queries. When a sub-query is being processed, parallelization techniques may be applied. In this paper, we focus on the scheduling issues of the sub-queries, rather t han the parallelization of the sub-queries themselves. Rules are formulated to guide the parallel query execution process. Our analysis shows that whe n there is no load skew, the serial scheduling strategy is preferred, other wise the parallel scheduling strategy should be used. (C) 1999 Elsevier Sci ence B.V. All lights reserved.