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Patent Title: System and method for hybrid hash join using over-partitioning to respond to database query

Assignee: IBM
Patent Number: US6226639
Issue Date: 05-01-2001
Application Number:
File Date:09-22-1998

Abstract: A system and method for joining a build table to a probe table in response to a query for data includes over partitioning the build table into "N" build partitions using a uniform hash function and writing the build partitions into main memory of a database computer. When the main memory becomes full, one or more partitions is selected as a victim partition to be written to disk storage, and the process continues until all build table rows or tuples have either been written into main memory or spilled to disk. Then, a packing algorithm is used to initially designate never-spilled partitions as "winners" and spilled partitions as "losers", and then to randomly select one or more winners for prospective swapping with one or more losers. The I/O savings associated with each prospective swap is determined and if any savings would be realized, the winners are designated as losers the losers are designated as winners. The swap determination can be made multiple times, e.g., 256, after which losers are moved entirely to disk and winners are moved entirely to memory. At the end of the swapping, probe table rows associated with winner partitions are joined to rows in the winner build partitions while probe table rows associated with loser partitions are spilled to disk. Then, the loser build partitions are written to main memory for joining with corresponding probe table partitions, to undertake the requested join of the build table and probe table in an I/O- and memory-efficient manner.


Link to USPTO

IBM Pledge dated 1/11/2005