VSAM Cardinal - e-vse.com · VSAM Cardinal Abstract This presentation addresses issues relevant to...
Transcript of VSAM Cardinal - e-vse.com · VSAM Cardinal Abstract This presentation addresses issues relevant to...
VSAM Cardinal Abstract This presentation addresses issues relevant to all z/OS enterprises that exploit VSAM. When the issues addressed by this presentation are ignored, unintentionally overlooked, or put on the back burner for higher priority tasks, both application- and system-level performance will suffer. The intent is to provide you with a systematic and automated approach to creating and maintaining high levels of integrity, productivity, and performance in your VSAM environment.
VSAM Cardinal Abstract, cont.
We will discuss how VSAM natively controls sharing of datasets and the impact on application performance, availability, and integrity of the underlying data. We will also address the challenges associated with establishing and maintaining a high-performance VSAM environment without having a negative impact on the productivity of the IT staff.
VSAM Sharing and Integrity • Challenge
ü VSAM allows only one program to update a dataset (with full integrity) § Can cause long batch cycles § Reduces the availability of online systems
– Manipulation of the SHAREOPTIONS parameter » Further reduces online availability » Negative impact on application performance
VSAM Sharing and Integrity • Band-Aids
ü Re-develop applications using a proprietary DBMS
ü Develop CICS transactions that perform batch functions
ü Create shadow databases ü Make batch programs open and close files ü Homegrown software for remote file access
(function shipping?)
VSAM Sharing and Integrity • Band-Aids
ü Manipulation of the SHAREOPTIONS parameter § Further reduces online availability § Negative impact on application performance § Four specific options with various levels of access and integrity
VSAM Sharing and Integrity • SHAREOPTION 1
ü Any number of OPENs for batch or online ü These OPENs must be read-only ü Only one program (or transaction) can open
for UPDATE (write) ü Provides complete integrity
VSAM Sharing and Integrity • SHAREOPTION 2
ü Any number of OPENs for batch or online ü These OPENs must be read only ü Only one program (or transaction) can open
for UPDATE (write) ü VSAM locks the CI, but users will have to
ENQ on the record key for integrity
VSAM Sharing and Integrity • SHAREOPTION 3
ü Completely shareable by anybody and everybody
ü Integrity? ü SHAREOPTION 3 applies to both cross-
region and cross-system integrity
VSAM Sharing and Integrity • SHAREOPTION 4
ü Completely shareable by everybody (READ and UPDATE)
ü SHAREOPTION 3 level integrity, use ENQ/DEQ for each I/O operation
ü SHAREOPTION 4 applies to both cross- region and cross-system integrity
VSAM Sharing and Integrity • Band-Aids
ü Locking § RLS could be used
– Enables CICS to do all writes – This might allow for reads – Read integrity is not guaranteed
» So again, user, do your own ENQs
VSAM Sharing and Integrity • The optimal approach
ü Control VSAM sharing with a transparent Intelligent File Management System (IFMS) § Intercepts, controls, and executes batch and online I/O requests § Could run in its own address space § Functions as the VSAM traffic cop with full data integrity
– Not limited by number of read/update users
IFMS in the Environment • Capitalizes on CICS’s multi-programming capabilities
• Transparently intercepts VSAM requests for files and performs I/O operations with integrity (batch and online)
• Two methods of communication ü LU 6.2 for remote file access ü XMS if both the batch job and CICS are
running on the same CPU
IFMS Environment
BATCH
Application Program
with IFMS Intercept
IFMS I/O
Manager and Online Interfaces
VTAM LU6.2
CICS
MVS Cross Memory Services
IFMS in the Environment • Complete data integrity
ü I/O is centralized within CICS ü Both CICS and batch jobs can update the
same file simultaneously • Total transparency
ü No programming changes ü No new interfaces to learn
• Selective SYNCpointing and Recovery (SSAR)
IFMS in the Environment • Control and flexibility
ü You define which jobs are impacted § You determine max number of jobs that may
simultaneously access CICS
ü Works within your security environment ü Dynamically suspend, restart, cancel, or
change the number of I/Os being sent to CICS by a given job
IFMS with SSAR • Needless to say, Tier 1 is the simplest to implement and is mostly suited for short-running jobs that do few updates. Tier 1 relies on CICS DTB for recovery.Tier 2 is straight forward, as well, but will need a basic understanding of journaling. Tier 3 will need some attention
IFMS with SSAR • The SYNC level field on the JOB MAINTENANCE screen identifies journaling (Tier 2) and is the number of CICS file ENQUEUEs allowed before a SYNCpoint is issued
IFMS with SSAR • With Tier 1 or 3, 0 (zero) is used • With Tier 2, CICS does not journal
ü Journaling is from within the IFMS
• Journaling is completely transparent to the application
IFMS with SSAR • Recovery (in Tier 2) is started using the journal
CICS
VSAM Files
Program A IFMS
Program B IFMS
IFMS
“A” Files
“B” Files
Journal
IFMS with SSAR • Unlike the prior two options, Tier 3 will require program modifications
• Tier 3 is best suited for long-running jobs
IFMS Solution Summary • Unlimited sharing with integrity
ü Total transparency ü No source code modifications
§ No recompiling of current code
ü No mods to existing system software ü No proprietary address spaces to support ü Support for all programming languages ü No new interfaces or commands to learn ü Easy installation, activation/deactivation
What about VSAM Performance? • VSAM is the most widely used access method in one form or another ü Dwindling amount of mainframe tuning expertise ü When properly tuned─very strong performer ü Without proper tuning
§ Online and batch performance suffers § Can lead to unnecessary processor and DASD
upgrades § Lost productivity performing file reorgs
What about VSAM Performance? • Improving VSAM performance
ü Identify obvious waste and inefficiencies § Run a FREECYLINDERS report § Run an EMPTY report § Run a “Not Updated Since 20xx” report
ü Analyzing the remaining legitimate datasets § Get professional help!
– Find a software solution that streamlines the process of analyzing and managing VSAM
» Design and allocate » Analyze » Reporting
VSAM Performance Summary
• VSAM tuning is critical ü Limited human resources are available
• A good software solution will support the major components of your VSAM environment ü Design/Allocate ü Analysis ü Recommendations