Abstract
Complex object-oriented queries generally consist of path expressions and explicit join operations. Since explicit join operations have been acknowledged 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 to 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 than the parallelization of the sub-queries themselves. Rules are formulated to guide the parallel query execution process. Our analysis shows that when there is no load skew, the serial scheduling strategy is preferred, otherwise the parallel scheduling strategy should be used.
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