IBM Systems Magazine, Mainframe - January/February 2014 - 32

TECH CORNER

Improving SYSOUT
PERFORMANCE
JES2 SAPI POST optimization can yield results

R

ecent reports of performance problems related to SYSOUT work selection
center around SYSOUT taking longer to process due to an outage in the
back-end SYSOUT processing. When it is eventually restarted, JES2 spends
so much CPU on SYSOUT selection that the system has trouble working through
the accumulated SYSOUT backlog.

Kevin Kathmann
is an advisory
software engineer
working in JES2
development since
2008. He has
worked more than
20 years with IBM.
Alexei Pytel
is an advisory
software engineer
working in z/OS
JES2 development
since 2007. He has
been with IBM for
19 years.
Steve Simonson
is a senior software
engineer working
in JES2 as a
developer since
2007. He has been
with IBM for
27 years.

JES2 performance statistics
show that for many installations,
SYSOUT work selection is a
significant part of JES2 CPU cost.
SYSOUT work selection happens
when a process such as a JES2
printer or an application using the
SAPI interface requests SYSOUT
from JES2.
The SYSOUT work selection has
two main parts:

characteristics and goes to sleep
(i.e., waits on an ECB). When new
SYSOUT work becomes available,
JES2 finds all waiting applications
with matching criteria and wakes
them up (i.e., posts the ECBs).
This is called SYSOUT POST
processing. In V2R1, this part of
SYSOUT work selection has also
been improved. This optimization
is described in this article.

1 When an application starts, it

A New Problem

requests ready-to-be-processed
work from JES2. This is called
SYSOUT GET processing. In
response to a GET request, JES2
scans the SYSOUT queues and
finds the SYSOUT that matches
criteria specified in the request.
Significant effort has been spent
in JES2 V2R1 to optimize GET
processing for SAPI applications.
This topic will be covered in a
future article.
2 When all readily available
work has been processed,
JES2 returns an indication to
the application that no more
SYSOUT with matching attributes
is available. At this point, the
application registers its interest
in the SYSOUT with certain

SYSOUT GET processing could
be compared to a database
query: Find a record (piece of
SYSOUT) that matches a query
(SYSOUT selection expression).
SYSOUT POST processing solves
an opposite problem. Given a
record (new piece of SYSOUT) and
a set of queries (processes with
their selection expressions), find
all queries that match this new
SYSOUT and wake up associated
applications.
Another way to describe this
problem is a subscription model.
A set of applications subscribes
to be notified when new SYSOUT
becomes available. Each
application has its own selection
expression and only wants to be

notified about pieces of SYSOUT
that match its criteria.
In prior releases of JES2 the
SYSOUT POST processing was
straightforward:

1 Look at each application
waiting for SYSOUT

2 Compare its selection criteria to
a new piece of SYSOUT

3 If there is a match, POST
associated ECB

32 // JANUARY/FEBRUARY 2014 ibmsystemsmag.com

The evaluation of a single
selection expression is not
particularly expensive. However,
this logic does not scale well.
As systems become larger, more
SYSOUT is processed by the
system and more applications are
waiting for SYSOUT. Therefore,
more CPU cycles are spent on
testing for a match between this
new SYSOUT against all selection
expressions. Something had to be
done to reduce this overhead.

The Solution-Selection
Expression Cache
Clearly, there was a need to
organize selection expressions
used by the applications in
such a way that the number of


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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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