Cache-based predicate handling for queries on XML data using uncorrelated path-based row sources

摘要

The approaches described herein provide an efficient way to process certain kinds of queries that retrieve XML data stored in an object-relational database. An XML query may include a predicate condition that joins two row sources. One or both of the row sources required for predicate evaluation may be path-based; that is, consume and produce rows of XMLType data. Such a path-based row source may be modified to use the predicate condition to filter the rows it generates so that only rows satisfying the predicate condition need to be further processed. A small cache structure introduced into the path-based row source may be used to optimize the evaluation of the predicate row. Once populated with row data, the cache structure may be reorganized to optimize the performance of predicate evaluation.

主权项

1. A computer-implemented method comprising:
computing a query against a collection of XML documents stored in one or more tables of a database by, at least in part, executing a plurality of row sources of a query execution plan, each row source of said plurality of row sources generating one or more output rows; wherein said plurality of row sources includes a path-based row source based on a path expression; wherein said query comprises a row predicate condition that specifies one or more conditions that output rows of said path-based row source must satisfy; wherein executing the path-based row source causes:
(a) identifying, based on said path expression, XML data from one or more input rows to said path-based row source;(b) filtering, based on said row predicate condition, said XML data from said one or more input rows to said path-based row source;(c) generating output rows that contain XML data based on said (a) identifying, based on said path expression, XML data from one or more input rows to said path-based row source and said (b) filtering, based on said row predicate condition, said XML data from said one or more input rows to said path-based row source.