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Efficient External Sorting Technique for Non-Synchronous DASD Operation

IP.com Disclosure Number: IPCOM000106214D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Archer, GD: AUTHOR [+6]

Abstract

One efficient DASD sort algorithm is known as Sort Blockset. This sort algorithm dynamically plans each I/O operation to minimize the elapsed time lost skipping from one DASD track to another. The design of the blockset technique depends on time-predictable synchronous operation between a system I/O channel and a DASD control unit. When using that technique in a non-synchronous I/O environment, it is not possible to maintain the same level of performance due to unpredictable variations in DASD-to-system operation timing that results in missed DASD rotations.

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Efficient External Sorting Technique for Non-Synchronous DASD Operation

      One efficient DASD sort algorithm is known as Sort Blockset.
This sort algorithm dynamically plans each I/O operation to minimize
the elapsed time lost skipping from one DASD track to another.  The
design of the blockset technique depends on time-predictable
synchronous operation between a system I/O channel and a DASD control
unit.  When using that technique in a non-synchronous I/O
environment, it is not possible to maintain the same level of
performance due to unpredictable variations in DASD-to-system
operation timing that results in missed DASD rotations.

      To alleviate this performance impact, ECKD* DASD command set
has added a Read Trackset operation code to the Locate Record
Extended command.  It defines a domain in which data transfer
commands will access data elements which need not be contiguous on
DASD but whose location is specified by values in the Locate Record
Extended parameter list.  Read Trackset prepares the control unit to
transfer a set of noncontiguous tracks to be read.  The control unit
is able to prefetch tracks of data and makes them available to the
channel by the time the data is requested.  Thus, a level of
performance is maintained as if the data were accessed contiguously.

      The extended parameter field of the Locate Record Extended
parameter list contains a bit map that represents a set of
sequentially addressed tracks within the defined...