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  • 7/27/2019 Who Just Killed My Db2 Gelb2003b


    Who Just Killed My DB2?!

    Ivan L. Gelb

    Gelb Information Systems Corp.

    Email: ivan@gelbis.com

    Phone: 732-303-1333

    @CMGA 2003 - Sydney

    DB2 for z/OS and S/390

    Insuring optimum DB2 service levels in the OS/390 environment is challenging because of not so

    obvious dependencies between the many subsystems. Performance biases introduced by systems

    tuners in z/OS - OS/390, CICS, and DB2 can dramatically affect the complexs service levels andtotal effective capacity. This presentation will describe how to focus DB2 environments tuning

    projects while insuring that the interdependent areas of z/OS, CICS, TSO and batch are optimized.

    Attendees will learn how to avoid being caught in unproductive finger pointing sessions by (a)

    insuring that subsystems are tuned with proper bias, (b) monitoring performance metrics that

    indicate the true illness or wellness of the complex, and (c) knowing what measures are available

    once the source of a service level problem is identified.

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    Basics of Performance Tuning

    DB2 Point of View

    z/OS - OS/390 Point of View

    CICS Point of View

    Pointing in the Right Directions

    We will focus on the latest systems versions: z/OS 1.4, CICS 2.2, DB2 6 8. The first four bullet

    point will show where, how, and what to look for, and the last point will show six examples that

    always cause contention among staff in different system and application areas. Following is oursession outline.

    Basics of Performance Tuning: (1) Is anyone complaining? (2) Where to begin?

    DB2 Point of View: (1) Eliminate bottlenecks; (2) Protect loved ones

    OS/390 Point of View: (1) Allocate resources: CPU, I/O, storage; (2) Definitions of relative

    priorities & their effects; (3) Protect loved ones (4) Who used, how much, of what, for howlong..

    CICS Point of View: (1) Eliminate bottlenecks; (2) Protect loved ones (3) Create throttles;

    Pointing in the Right Directions (3 CPU and 2 I/O cases): (1) Starved for CPU; (2) CICS region

    saturated; (3) DPMODE = What? (4) Buffer Pools (5) High I/O Service Time

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    Basics of Performance Tuning

    Is anyone complaining?

    Do YOU want to prevent complaints?

    Where to begin?

    Ask these questions


    The following are trade or service marks of the IBM Corporation: CICS, CICS TS , CICSPlex,

    DB2, IBM, MVS, OS/390, z/OS, Sysplex, Parallel Sysplex. Any omissions are purely unintended.


    All of the information in this document is tried and true. However, this fact alone cannot guarantee

    that you can get the same results at your place and with your skills. In fact, some of this advice can

    be hurtful if it is misused and misunderstood. As with all kinds of analysis, anything you may hear

    or read can be understood and misunderstood in many ways that may seem contradictory to you. In

    this regard, a further and associated contradictory element requires considerable systems analysis

    and trade-off studies to arrive at the structural design, based on rigorous system engineering

    concepts. By combining advice and certain experiences, any fully integrated performance testprogram is weakly equivalent to any subsystem compatibility testing designed to eschew

    obfuscation. Gelb Information Systems Corporation, Ivan Gelb and any one found anywhere

    assume no responsibility for this informations accuracy, completeness or suitability for any

    purpose. Anyone attempting to adapt these techniques to their own environments anywhere do so

    completely at their own risk. ;-)

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    Is Anyone Complaining?

    If YES, why?

    Some service is slow and/or failing to meet service level

    objectives (be sure that objectives are rational!)

    Response time is OK, but not enough is completed

    For either case:

    Total Delays = Response Times Measured Service Times

    What is Total Delays / Total Response Time ratio? < .50 is OK

    but it up to doubles response time

    The ratio acceptable to your site will depend on service level


    First, we should not be waiting for complaints even though it helps justify the existence of our job.

    Be effectively proactive, and they may wonder why tuning is needed.

    Being proactive includes at least the following minimum activites:

    -Profiles of all workloads so you can tell if behavior changes,

    -Tracking of past and future changes in system software, hardware, and applications, and

    -Profiles of utilization by business units of work is the most effective way to do all this.

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    Do YOU Want to Prevent Complaints?

    We consider WAITING for

    complaints a CLS (Career

    Limiting Strategy).

    Your actions plan should

    prevent complaints.

    If you do your job real well,

    some may wonder if you are


    Wait for or prevent complaints,the plan of action is the same.



    Adjust 1Thing!



    This is a bit of philosophy here.

    The practical issue is that for well managed shops the best practice is to work on prevention of


    Performance management is a cyclical activity.

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    Where to begin - 1

    Evaluate performance:

    Inside DB2

    Outside DB2

    Inside DB2 (not our sessions focus) Obtain / establish Service Level Agreements (SLAs) for

    business critical work.

    Without SLA-s, identify what is reasonable response time given

    the service time profile of the workload.

    Collect accounting trace class 2 and 3 for best information on

    externally caused delays

    Class 1 and 3 accounting traces reveal the tasks complete

    activity (we will review a summary report from DB2 PM)

    A DB2 performance evaluation should always start from inside out. Simply, you do not want to be

    found with your homework not done.

    We are going to look at reports in our quest for who killed your DB2 performance that will showboth types of measurements: indicators of problems inside DB2, and indicators that factors outside

    DB2 are cause of degradation.

    This session will drive towards identifying situations where the outside factors are causing the


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    Where to begin - 2

    Outside DB2 analysis focuses on eliminating factors that

    degrade DB2s performance

    Search for hints inside DB2 that outside factors may be

    cause of problems:

    Wait for

    CPU due to higher priority work

    CPU due to LPAR management of weights

    Central storage

    Long basic I/O service times

    > 3 msec for cached writes

    > 5 msec for cached reads

    Long non-service time components of I/O servicePEND, Disconnect, Device Busy, Control Unit Busy

    As you can see from the list on the slide, delays come in many flavors.

    We will show reports and recommend where to look to isolate causes for the delays.

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    Where to begin - 3

    Prepare profiles of resource utilization by workload:

    CPU, I/O, processing parallelism, processor storage, network time

    Any latent demand?

    If YES, what makes it up? Work you HAVE to care about or NOT?

    Easy to tell if there is some latent demand see RMF CPU Activityreport

    Harder to tell who it is waiting for CPU

    Where to look?

    RMF Workload, CPU, device, storage activity reports

    SMF file activity reports

    CICS & DB2 subsystems reports

    CICS & DB2 subsystems traces are last resort, but most time

    consuming to analyze and most trustworthy

    This is an outline of where to begin analysis. Samples of how this is done follow later in


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    Ask These Questions - 1

    What is your class 2 elapsed time (C2ET)?

    How much of C2ET is:

    Wait for CPU dispatch?

    MVS Overhead? I/O-s related wait?

    System page-ins?

    Which DASD devices are not providing good performance?

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    Ask These Questions - 2

    Other classic questions you should not forget to ask, but willnot be discussed in much detail in our session today:

    What is your system I/O rate/Second for:

    Each pool?

    Critical objects?

    What is your average Synch I/O elapsed time?

    What are your buffer pool hit ratios?

    Is you SQL coding effective?

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    DB2 Point of View

    Eliminate bottlenecks

    Protect loved ones

    Identify Suspect Areas

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    2003 GIS Corp . - www.gelbi