摘要:
Techniques are described for preserving the original insignificant white space of XML data. The techniques may be used in combination with compact XML data storage formats, such as binary XML, to preserve the insignificant white space without requiring as much storage space as uncompressed formats. White space opcodes/operand pairs are described for representing white space characters and white space patterns. The white space opcode/operand pairs represent the white space in binary XML, are use to generate the original white space when the binary XML is decoded back to textual XML data.
摘要:
Techniques are described for preserving the original insignificant white space of XML data. The techniques may be used in combination with compact XML data storage formats, such as binary XML, to preserve the insignificant white space without requiring as much storage space as uncompressed formats. White space opcodes/operand pairs are described for representing white space characters and white space patterns. The white space opcode/operand pairs represent the white space in binary XML, are use to generate the original white space when the binary XML is decoded back to textual XML data.
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. A technique determines whether a query comprises a plurality of iteration expressions that exhibit a particular relationship to one another, and if so, re-writes the query and produces an optimized query execution plan. The query execution plan specifies an XPath-based row source with caching enabled. A very small cache structure is used, and reference locators are stored in the cache that point into binary-encoded data rather than copying XMLType data into the cache. Row data may be cached on the first use of the path-based row source and re-used in subsequent requests for rows. Once there is a subsequent request for rows from the optimized path-based row source, the cache may be reorganized to efficiently produce the rows of the row source.
摘要:
Techniques are provided for ensuring lexical fidelity when an XML document is stored in a binary format. Operations, on the XML data, that would cause the loss of lexical fidelity between the original XML document and the binary-encoded version of the XML document are not performed. Such operations include the removal of unnecessary whitespace characters, certain data type conversions, CRLF normalization, the “collapsing” of two-tag empty elements into a single tag empty element, and the replacing of entity references or numeric character references with another value. An XML schema, to which the XML document conforms, may indicate that the XML document is to be stored in a lexical fidelity mode. Additionally, or alternatively, the database statement that (when executed) causes the XML document to be stored in a binary format may so indicate.
摘要:
A mechanism is provided for improving the performance of particular database queries operating on a view comprising binary-encoded XML. The key to improving performance is to determine whether a XML index is available to improve the computation of XPath data before deriving an optimized execution plan for a particular query. When a XML index is not available to help expedite the computation of binary-encoded XML, then deferring the computation of the XPath data until after the view merge stage avoids unnecessary computation of XPaths that are part of the view but not needed for the particular query.
摘要:
A method for storing XML documents a hybrid navigation/streaming format is provided to allow efficient storage and processing of queries on the XML data that provides the benefits of both navigation and streaming and ameliorates the disadvantages of each. Each XML document to be stored is independently analyzed to determine a combination of navigable and streamable storage format that optimizes the processing of the data for anticipated access patterns.
摘要:
A method for storing XML documents a hybrid navigation/streaming format is provided to allow efficient storage and processing of queries on the XML data that provides the benefits of both navigation and streaming and ameliorates the disadvantages of each. Each XML document to be stored is independently analyzed to determine a combination of navigable and streamable storage format that optimizes the processing of the data for anticipated access patterns.
摘要:
The approaches described herein provide an efficient way for a database server to process certain kinds of queries over XML data stored in an object-relational database that require the evaluation of a predicate expression with one or more path-based operands. A predicate expression part of a XQuery or SQL WHERE clause that returns a boolean value. A database server first determines whether the query qualifies for this particular kind of optimization, then rewrites the query using an enhanced query operator syntax for specifying the predicate expression to be evaluated. The enhanced query operator subsumes the work of a second path-based query operator, resulting in the suppression of the WHERE EXISTS subquery. The rewritten query operator is used to generate a query execution plan that provides for several query execution optimizations.
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.
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. A technique determines whether a query comprises a plurality of iteration expressions that exhibit a particular relationship to one another, and if so, re-writes the query and produces an optimized query execution plan. The query execution plan specifies an XPath-based row source with caching enabled. A very small cache structure is used, and reference locators are stored in the cache that point into binary-encoded data rather than copying XMLType data into the cache. Row data may be cached on the first use of the path-based row source and re-used in subsequent requests for rows. Once there is a subsequent request for rows from the optimized path-based row source, the cache may be reorganized to efficiently produce the rows of the row source.