Browse Prior Art Database

Multi-System Locking Facility Using Shared DASD

IP.com Disclosure Number: IPCOM000105927D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 6 page(s) / 238K

Publishing Venue

IBM

Related People

Kearney, JJ: AUTHOR

Abstract

A method for implementing logical locks utilizing a standard shared DASD. These locks represent objects, that is files, which typically do not reside on the locking DASD so the locks are not on the access path to the objects. Since a DASD is used to contain the locks, the primary advantage of the subject invention is a way to avoid the performance penalty of DASD rotational delays, a problem which does not exist in other environments. The present state of the art for implementing logical locks on a DASD requires at least two passes at the lock data on the device, with at least one intervening rotation. According to the present invention, only one pass over the lock data is required, which is a considerable performance and improvement.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 27% of the total text.

Multi-System Locking Facility Using Shared DASD

      A method for implementing logical locks utilizing a standard
shared DASD.  These locks represent objects, that is files, which
typically do not reside on the locking DASD so the locks are not on
the access path to the objects.  Since a DASD is used to contain the
locks, the primary advantage of the subject invention is a way to
avoid the performance penalty of DASD rotational delays, a problem
which does not exist in other environments.  The present state of the
art for implementing logical locks on a DASD requires at least two
passes at the lock data on the device, with at least one intervening
rotation.  According to the present invention, only one pass over the
lock data is required, which is a considerable performance and
improvement.

      Overview of Multi-System Locking Facility using Shared DASD -
This locking facility has the following characteristics.  It supports
a moderate number of global, exclusive locks with queueing.  The
facility supports locking at the system level, as opposed to the
process level; i.e., requestors are systems.  It preserves the
integrity of lock states in the event of the failure of the lock
device, and permits alternate devices to be dynamically substituted.
The facility provides acceptable performance, and it requires only
standard DASD hardware capabilities.

      Typical DASD locking mechanisms are of the RESERVE/READ/UPDATE/
WRITE/RELEASE variety which require two passes at the lock data.  The
reserve operation locks the entire device to the one system, the
current lock data is read, the data is processed and modified, the
updated data is rewritten to the device when the data comes around
again, and finally the device is replaced.  Obtaining a lock using
this approach requires more than a complete rotation of the device,
and the device is also unavailable to other systems for the entire
time of the locking operation.  By way of contrast, the primary
innovation in this locking facility is the ability to process a lock
request in the time needed for only one pass of the lock data under
the read/write head of the DASD device.  Furthermore, this approach
does not require the device to be reserved.  Therefore, the amount of
time the device is monopolized by a locking operation is essentially
only the time the lock data is under the read/write mechanism.  The
performance implications of this approach in a multi-system
environment will be discussed later.

      Functional Description of the Locking Facility - The global
locks are contained in a specially formatted dataset on the lock
device.  Each lock actually consists of a set of consecutive short
records (called a lockset) with one record in the lockset for each
system in the configuration.  For example, in a configuration of four
systems locks would each be represented by locksets formatted as
shown in Fig. 1.  Each track contains multiple locks, the number of
which...