| 摘要 |
A method, apparatus, and article of manufacture for generating statistics for use by a relational database management system. A global aggregate spool is generated for each of a plurality of partitions of a subject table that are spread across a plurality of processing units of a computer system. Each of the global aggregate spools is scanned to generate summary records. The summary records are then merged to generate interval records for a compressed histogram of the subject table, wherein the compressed histogram includes both equal-height intervals and high-biased intervals. The compressed histogram can then be analyzed to estimate the cardinality associated with one or more search conditions of a user query or other SQL statement. Compared to a strictly equal-height histogram, the compressed histogram allows the relational database management system to more accurately estimate the cardinality associated with various search conditions. As a result, the relational database management system can better optimize the execution of the user query.
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