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Methodology for increasing the average run length produced by replacement selection strategy in a system consisting of multiple, independent memory buffers
| Details |
Inventors: Turek, John J. E.; Yu, Philip S.;
Assignee: International Business Machines Corporation (Armonk, NY)
Primary Examiner: Black; Thomas G.
Assistant Examiner: Wang; Peter Y.
Attorney, Agent or Firm: Drumheller; Ronald L., Ludwin; Richard M.
A range of key values is partitioned into a plurality of key subranges equal in number to the number of record storage areas available for the sort. One of the key subranges is then assigned to each of the record storage areas and records to be sorted are transferred to the record storage areas in accordance with a sort key value within each record and the key subrange assigned to each of the record storage areas. Whenever a record is transferred to a filled record storage area, a record from the filled record storage area is transferred to an output string, namely the record that has the lowest key value that is not lower than the last record added to the output string of the filled record storage area. Whenever a record is transferred from a filled record storage area to the output string and has a higher key value than the last record added to said output string, the key subrange for the filled record storage area is updated to begin at the higher key value, and, the ending key value of the next lower subrange is increased to a new value which is not lower than the higher key value. |
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DETAILED DESCRIPTION In light of the foregoing, there is provided an external parallel sort method for use in a computer system having a plurality of record storage areas available for sorting.
In accordance with the method, a range of key values are partitioned into a plurality of key subranges equal in number to the number of record storage areas available for the sort.
One of the key subranges is then assigned to each of the record storage areas and a group of records to be sorted is transferred to the record storage areas in accordance with a sort key value within each record and the key subrange assigned to each of the record storage areas.
When a record is transferred to a filled record storage area, a record from the filled record storage area is transferred to an output string.
The record transferred to the output string is the record that has the lowest key value that is not lower than the last record added to the output string of the filled record storage area.
When a record is transferred from a filled record storage area to the output string and has a higher key value than the last record added to said output string, the key subrange for the filled record storage area is updated to begin at the higher key value.
Further, when a key subrange is updated to begin at a higher key value than an ending key value of the next lower subrange, the ending key value of the next lower subrange is increased to a new value which is not lower than the higher key value.
A subrange is considered to be lower than another subrange when the lowest value key it contains is lower than the lowest value key contained in the other subrange.
When creating original sorted runs in standard sorting techniques, each processor operates in isolation.
Assuming randomly organized data, the expected length of the original sorted runs produced by an algorithm such as that given by Iyer, Ricardi, and Varman will be around 2 m where m is the number of tuples that can be stored in the memory of each processor.
As the number of processors P increases 2 m becomes significantly less than the total number of tuples Pm that can be held in the memory of the system
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I/O Systems 
