Browse Prior Art Database

Method of Table Update Serialization without Accessor Quiescence

IP.com Disclosure Number: IPCOM000108911D
Original Publication Date: 1992-Jul-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Benson, SM: AUTHOR

Abstract

When making changes to a resource such as a table, it is necessary to control access so that inconsistent information is not obtained. When several items in the resource must be changed at once to prevent inconsistent information, it is necessary to stop accesses to the resource through some locking mechanism. When the resource is frequently accessed, this can present some performance problems. This invention solves the problem of making changes to the resource without quiescing accessors of the resource and still ensuring data integrity.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Method of Table Update Serialization without Accessor Quiescence

       When making changes to a resource such as a table, it is
necessary to control access so that inconsistent information is not
obtained.  When several items in the resource must be changed at once
to prevent inconsistent information, it is necessary to stop accesses
to the resource through some locking mechanism.  When the resource is
frequently accessed, this can present some performance problems.
This invention solves the problem of making changes to the resource
without quiescing accessors of the resource and still ensuring data
integrity.

      This invention solves the above problem by introducing a
parallel copy of the resource and maintaining information about the
accessors to both resources.  The parallel resource has the desired
changes made and any process which desires information from the
resource after the parallel resource has been made active will obtain
the information from the new resource.  Any existing process which
has previously obtained information from the old resource will
continue to obtain any additional information from that old resource
to ensure data consistency.  Once the old resource is no longer being
accessed, i.e., all of the processes accessing it have completed, it
can be disposed of.  An access controller maintains the information
about how many accessors are currently using both resources and any
request for access to the resource will be made through the
controller which will present the requester with the correct resource
to use.

      The specific area that this invention is applied to is the
Allocation Eligible Device Table (EDT).  The EDT is a mapping of the
logical relation of unit names to pools of devices.  The unit names
are defined statically to contain specific devices in the
configuration.  When a job requests an allocation, one of the
possible inputs is the UNIT parameter of the DD statement.  Through
the UNIT parameter, the job requests an available device from the
pool of devices defined to the unit name specified.  Allocation uses
the EDT to find out which devices are eligible to satisfy the
request.  Since devices...