VSAM System Software
In the IBM mainframe environment an access method is
required for an application program written in a procedural or low-level
language to access data on a DASD: Direct Access Service Device. The
role of an access method includes setting record size, determining
available disk space for record storage, writing data to disk, locating
data on disk, and retrieving data from the disk. Without a reliable
access method, the programmer would be required to make calculations and
write the code in each program. The VSAM code in legacy programming
languages - primarily COBOL, Assembler, and PL/1 - is a component of
operational infrastructure specific to the client's IBM mainframe
operating system - z/OS or z/VSE.
| IBM Mainframe Software Environment |
| |
 |
In the late 1970’s IBM introduced VSAM: Virtual
Storage Access as its new access method; replacing ISAM and BDAM. VSAM
added functionality, device independence, and improved performance. It
was also easier to use. There have been numerous improvements made to
VSAM and it is still integral mainframe system software. VSAM is
used extensively in the CICS Transaction Server environment to provide
recoverability, data locking, and integrity to source data. Sharing of
VSAM data among CICS regions is done with VSAM RLS: Record-Level
Sharing; this adds record caching and record locking. Logging and commit
processing remains the responsibility of CICS. This means that sharing
of VSAM data outside a CICS environment will be restricted.
VSAM has been the workhorse access method for IBM’s
z/OS and z/VSE evolutionary operating system's and system software
products: IMS, CICS, and DB2. Although the role of VSAM and its relative
importance has changed with the emergence of DB2 and web enablement
technologies, a knowledge of VSAM is important for optimizing
performance and balancing the processing of input/output.
VSAM now uses some of the newer hardware technology to improve
performance. In a multi-extent, multi-volume VSAM dataset processed in
sequential access, processing does not allow for any type of parallelism
for I/O operations among the volumes. This means that when an I/O
operation is executed for an extent in a volume, no other I/O activity
from the same task or same dataset is scheduled to the other volumes. In
a situation where I/O is the major bottleneck, and there are available
resources in the channel subsystem and controllers, it is a waste of
these resources.
Data striping addresses this sequential access
performance problem by adding two modifications to the traditional data
organization:
- The records are not placed in key ranges
along the volumes; instead they are organized in stripes.
- Parallel I/O operations, in the form of control
intervals are scheduled to sequential stripes on different volumes.
Enhancements have been made to VSAM with
the IBM z/OS V1.10 operating system. The VSAM CA Control Area Reclaim
capability provides applications which use VSAM KSDS key-sequenced
datasets with improved availability through minimizing outages required
for data defragmentation and reorganization. Disk space utilization also
is better. CETi Technology Partners are evaluating IBM product
announcements regarding performance, which have been reported to be as
high as a 44% improvement for VSAM-based workloads.
VSAM
Training by SYS-ED
Since 1980 ,
SYS-ED has been a leader in VSAM training and educational consultancy.
We have a track record for developing the knowledge and skillset
required by
Fortune 1000 companies
,
government municipalities,
healthcare providers,
and
consulting firms
to address
specific operational objectives. If
your organization outsourced the optimization of its VSAM coding to
consulting firms in the 1980’s, it more than likely was SYS-ED which
trained the personnel that did the actual work.
The sample programs and
exercises were developed, updated, and tailored to teach VSAM in
evolutionary MVS and VSE environments with legacy programming languages.
Our consultancy derived content and VSAM courses have served as a
framework from which
industry standard text books
have been refined - subject matter, sample programs, and exercises - to
ensure that they addressed "real world" work environments. In addition
to VSAM, we also provide training on the
IBM and third-party mainframe utilities and
development tools
inclusive of examples and integrated exercises on
Compuware and Computer Associates software.
When information technology professionals
leave a SYS-ED VSAM course, they have the skeleton programs,
documentation, training aids, and supervised hands-on experience to
efficiently code and maintain programs back on the job. Case and point,
we encourage clients to provide us with listcats from their production
systems prior to attending a class. We analyze and interpret that
information and teach the concepts and techniques required to make VSAM
performance optimization a reality.
The value added service to a SYS-ED VSAM
course is the educational consultancy we can provide. Case and
point, if your organization outsourced its CICS and VSAM coding and
program maintenance to consulting companies in the 1980’s, it more
than likely was SYS-ED which trained the consultants who did the
actual design and coding!
IBM's information agenda is built on
its proprietary operating systems and system software. Its
foundation is to simplify, collaborate, reuse, and standardize. SYS-ED's
mainframe course offerings, training programs, and software specific
websites have been designed to add value-added service to this
strategy and IBM's cloud computing initiatives.
1- Delivery of content through multiple delivery
medium as part of a collaborative environment for integrating data at a business
level.
2- Student hand-outs, reference guides, and
validation assessment for training human resources that leverage existing
investments in software infrastructure.
3- Application development accelerators in the
form of industry and client-specific training aids, examples, templates, and
data modeling.
4- Support services in the form of technology
updates, knowledge base, answers to questions, and tailored documentation in
hybrid and interrelated information technology.
The VSAM courseware and training aids
that we provide as part of our instructor-led courses are highly
respected. The content and diagrams reflect a purposeful examination of
program logic, access methods services, and sample programs which have
been validated on consulting projects. SYS-ED's VSAM courseware is
updated with information from FAQ's frequently asked questions,
technology updates, and CETi knowledge base. Given the scarcity of up to
date industry standard VSAM text books, our courseware serves a valuable
function as a reference manual.
Upon completion of a
instructor-led course at the client location, it is standard policy to
organize content for future utilization in a web-based training
infrastructure.
|
