IBM Systems Magazine, Mainframe - January/February 2014 - 33

expressions considered for each
SYSOUT can be reduced. For
example, if new SYSOUT is in
class A, looking at expressions
that explicitly call out class B is
unnecessary.
What complicates the task
is that JES2 provides many
SYSOUT attributes that can be
used to select SYSOUT. Selection
expressions can use any number
of these attributes. It could be
possible to organize a set of
selection expressions based
on their syntax trees. However,
the processing involved is very
complex and would be costly.
Instead, another approach was
taken. As selection expressions
are considered during SYSOUT
POST processing, information
about them is saved in a cache.
In this way, when a new SYSOUT
arrives with similar attributes, the
results from cache can be used
instead of reconsidering these
expressions repeatedly.
Data in the cache is organized
in a binary tree and indexed by
a set of SYSOUT attributes (e.g.,
SYSOUT class and destination).
Initially, the cache is empty.
When new work arrives, SYSOUT
POST processing extracts a set of
attributes from new SYSOUT and
creates a cache node. Then each
selection expression is evaluated
and a determination is made
whether it is compatible with the
cache configuration and whether
it matches this new SYSOUT:
à Ã([SUHVVLRQVÃWKDWÃDUHÃQRWÃ
Ā
compatible are saved in a
special part of cache.
Ā
à Ã([SUHVVLRQVÃWKDWÃDUHÃ
compatible and match the node
are saved in the cache node.
Ā
à Ã([SUHVVLRQVÃWKDWÃDUHÃ
compatible but do not match
the node are ignored.
When new SYSOUT arrives,
incompatible expressions must

be evaluated as if no cache exists
because no useful information
can be saved about them. If
matches are found, associated
applications are awoken.
After that, a set of attributes is
extracted from this new SYSOUT.
The binary tree in the cache
is searched for a cache node
matching these attributes. All
expressions saved in this cache
node are known to be compatible
and matching, so it is unnecessary
to re-evaluate them, allowing
the associated applications to be
awoken without delay.

Managing POST Cache
In V2R1, the optimization for
the SYSOUT POST processing
is provided only for SAPI
applications. The support is

significant reduction in CPU
overhead, because this solution
scales better as the number of
applications grows.

The Importance of
Cache Configuration
A key concept for the functioning
of the cache is the compatibility
between a selection expression
and the cache configuration. Cache
configuration is defined by the set
of SYSOUT attributes chosen to
organize the data in the cache.
A selection expression is
compatible with the cache if
the SYSOUT attributes, used by
the selection expression, are a
subset of attributes used in the
cache configuration. If a selection
expression is not compatible, it
must always be evaluated for each

For cache to provide the most optimization
of the SYSOUT POST processing, the SYSOUT
attributes to be used must be carefully chosen.
activated on a member basis
via new SAPI_OPT keyword
on $TOUTDEF command or
OUTDEF initialization statement.
SAPI_OPT=YES enables the cache.
Cache can be disabled at any time
by SAPI_OPT=NO. The default is
SAPI_OPT=NO.
When SYSOUT POST optimization is turned on, the only
noticeable change in behavior is
better performance. The cache
does require some additional CPU
cycles for maintenance when new
applications start and connect
to JES2. After this initial phase,
cache fills in and begins to benefit
POST processing for new pieces of
SYSOUT as they become available.
In the worst case, when most
or all applications use selection
expressions that cannot benefit
from the cache, the CPU overhead
will essentially be the same as
without the cache. In the best
case, the cache will provide

new SYSOUT. Applications that use
such expressions won't experience
any benefit from the cache.
For cache to provide the most
optimization of the SYSOUT POST
processing, the SYSOUT attributes
to be used must be carefully
chosen. Too few attributes
will make too many selection
expressions incompatible and
will send them to the "always
evaluate" list. Too many attributes
will provide better selectivity
but will require additional main
storage and CPU time for the
cache maintenance.
The shipped cache configuration uses three SYSOUT attributes:
class, destination and disposition.
This combination was selected
based on analysis of common
selections used by SAPI applications. For optimal performance,
SAPI applications should try to
use some combination of these
selection attributes.
ibmsystemsmag.com JANUARY/FEBRUARY 2014 // 33


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IBM Systems Magazine, Mainframe - January/February 2014

Table of Contents for the Digital Edition of IBM Systems Magazine, Mainframe - January/February 2014

Table of Contents
Editor's Desk: The father of innovation
IBM Perspective: Mainframe innovation continues
Trends: RDz family of tools helps organizations address new paradigms and business expectations
IT Today: Flash Express integrates secure, high-performance storage within System z
Case Study: Weather or Not: Met Office makes a cost-conscious and test-driven decision to consolidate Linux instances on the mainframe
Cover Story: The System z influence: How mainframe innovations have helped shape and reshape the IT world
Feature: Always moving forward: IBM's System z platform has many more tricks up its sleeve
Tech Corner: JES2 SAPI POST optimization can yield results
How To: How to successfully implement zBX hybrid computing
Solutions: Attunity Replicate 2.1, InSync Plugin, Storage Director 4.1
Stop Run: Coin collecting and history fascinate mainframe strategist
Reference Point - Global Events, Education, Resources for Mainframe
2014 Mainframe Solutions Edition Product Index
IBM Systems Magazine, Mainframe - January/February 2014 - Intro
IBM Systems Magazine, Mainframe - January/February 2014 - Cover1
IBM Systems Magazine, Mainframe - January/February 2014 - Cover2
IBM Systems Magazine, Mainframe - January/February 2014 - 1
IBM Systems Magazine, Mainframe - January/February 2014 - Table of Contents
IBM Systems Magazine, Mainframe - January/February 2014 - 3
IBM Systems Magazine, Mainframe - January/February 2014 - 4
IBM Systems Magazine, Mainframe - January/February 2014 - 5
IBM Systems Magazine, Mainframe - January/February 2014 - Editor's Desk: The father of innovation
IBM Systems Magazine, Mainframe - January/February 2014 - 7
IBM Systems Magazine, Mainframe - January/February 2014 - IBM Perspective: Mainframe innovation continues
IBM Systems Magazine, Mainframe - January/February 2014 - 9
IBM Systems Magazine, Mainframe - January/February 2014 - Trends: RDz family of tools helps organizations address new paradigms and business expectations
IBM Systems Magazine, Mainframe - January/February 2014 - 11
IBM Systems Magazine, Mainframe - January/February 2014 - 12
IBM Systems Magazine, Mainframe - January/February 2014 - 13
IBM Systems Magazine, Mainframe - January/February 2014 - IT Today: Flash Express integrates secure, high-performance storage within System z
IBM Systems Magazine, Mainframe - January/February 2014 - 15
IBM Systems Magazine, Mainframe - January/February 2014 - 16
IBM Systems Magazine, Mainframe - January/February 2014 - 17
IBM Systems Magazine, Mainframe - January/February 2014 - Case Study: Weather or Not: Met Office makes a cost-conscious and test-driven decision to consolidate Linux instances on the mainframe
IBM Systems Magazine, Mainframe - January/February 2014 - 19
IBM Systems Magazine, Mainframe - January/February 2014 - 20
IBM Systems Magazine, Mainframe - January/February 2014 - 21
IBM Systems Magazine, Mainframe - January/February 2014 - Cover Story: The System z influence: How mainframe innovations have helped shape and reshape the IT world
IBM Systems Magazine, Mainframe - January/February 2014 - 23
IBM Systems Magazine, Mainframe - January/February 2014 - 24
IBM Systems Magazine, Mainframe - January/February 2014 - 25
IBM Systems Magazine, Mainframe - January/February 2014 - 26
IBM Systems Magazine, Mainframe - January/February 2014 - 27
IBM Systems Magazine, Mainframe - January/February 2014 - Feature: Always moving forward: IBM's System z platform has many more tricks up its sleeve
IBM Systems Magazine, Mainframe - January/February 2014 - 29
IBM Systems Magazine, Mainframe - January/February 2014 - 30
IBM Systems Magazine, Mainframe - January/February 2014 - 31
IBM Systems Magazine, Mainframe - January/February 2014 - Tech Corner: JES2 SAPI POST optimization can yield results
IBM Systems Magazine, Mainframe - January/February 2014 - 33
IBM Systems Magazine, Mainframe - January/February 2014 - How To: How to successfully implement zBX hybrid computing
IBM Systems Magazine, Mainframe - January/February 2014 - 35
IBM Systems Magazine, Mainframe - January/February 2014 - 36
IBM Systems Magazine, Mainframe - January/February 2014 - 37
IBM Systems Magazine, Mainframe - January/February 2014 - Solutions: Attunity Replicate 2.1, InSync Plugin, Storage Director 4.1
IBM Systems Magazine, Mainframe - January/February 2014 - 39
IBM Systems Magazine, Mainframe - January/February 2014 - Stop Run: Coin collecting and history fascinate mainframe strategist
IBM Systems Magazine, Mainframe - January/February 2014 - Cover3
IBM Systems Magazine, Mainframe - January/February 2014 - Cover4
IBM Systems Magazine, Mainframe - January/February 2014 - Reference Point - Global Events, Education, Resources for Mainframe
IBM Systems Magazine, Mainframe - January/February 2014 - 2014 Mainframe Solutions Edition Product Index
IBM Systems Magazine, Mainframe - January/February 2014 - SE2
IBM Systems Magazine, Mainframe - January/February 2014 - SE3
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