Browse Prior Art Database

Dynamically Shrink a Page Set While in Use by Many Applications

IP.com Disclosure Number: IPCOM000122869D
Original Publication Date: 1998-Jan-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 86K

Publishing Venue

IBM

Related People

Belding, GP: AUTHOR [+3]

Abstract

A Message Queuing system, such as IBM's MQSeriesR* system, has to hold any number of messages, of any size up to (currently) four megabytes, for an unknown period of time. Disk data sets, called page sets, are provided for storage of messages in queues. Messages are put onto and removed from the queues by customer applications at arbitrary times.

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This is the abbreviated version, containing approximately 52% of the total text.

Dynamically Shrink a Page Set While in Use by Many Applications

      A Message Queuing system, such as IBM's MQSeriesR* system, has
to hold any number of messages, of any size up to (currently) four
megabytes, for an unknown period of time.  Disk data sets, called
page sets, are provided for storage of messages in queues.  Messages
are put onto and removed from the queues by customer applications at
arbitrary times.

      Customers are given the task of deciding what size of page
sets are initially required.  If they underestimate the size
required, it is possible to dynamically expand the size of the page
sets, while the system is up and running and many applications are
using the expanding Page Set.

      Once a page set has been dynamically expanded, possibly up to
123 times, and all the messages have been retrieved, the customer is
left with, in some cases, very large empty page sets.  If reduction
of the size of these page sets is desired, this could only be done by
stopping the Message Queuing system, and performing a manual
procedure.  Customers require systems to be available for 24 hours a
day, 7 days a week, and 365 days a year.  Online data set
re-organization is  thus preferable to offline, complex, manual
procedures.

      An MQSeries for MVS/ESA* page set is a VSAM LINEAR disk data
set that consists solely of 4K long data areas that we manage, called
pages.

      Physically, this data set comprises a primary extent on disk,
and up to 123 secondary extents.  Each extent occupies a different
area on one disk drive.  (The page set as a whole can be spread
across multiple disk volumes, but each extent is entirely contained
on one disk).  These physical extents are typically not contiguous.
Despite this physical layout to the MQ system, the page set logically
occupies a range of storage, holding bytes 0 to 4 gigabytes, each
page being identified by a relative block address.  The currently
highest allocated  RBA is always known to the system.

      The first two pages in the data set are not available for
message storage and the second page contains a space map identifyi...