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Updated: 11 December 1998

OpenVMS System Manager's Manual


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15.15.3 Using SYSGEN

Compaq recommends that you use AUTOGEN to create and change page, swap, and dump files. AUTOGEN invokes the System Generation utility (SYSGEN) to create or change the files. However, in an emergency, you can use SYSGEN to directly change the size of page, swap and dump files. For example, if you see that page file space is becoming dangerously low, you might use SYSGEN to quickly add page file space to prevent the system from hanging.

Note

The SWPFILCNT and PAGFILCNT system parameters limit the number of swap and page files that the system installs. Refer to the OpenVMS System Management Utilities Reference Manual for more information.

How to Perform This Task

  1. Determine the location and appropriate size of the files. For information, see Section 15.4.
  2. Invoke SYSGEN and enter the CREATE command in the following format:

    CREATE file-spec/SIZE=block-count 
    


    where:
    file-spec specifies the full file specification.
    block-count specifies the size of the file in blocks.
    If the file you specify already exists and the size you specify is larger than the existing file, the command extends the existing file. If the file you specify already exists and the size you specify is smaller than the existing file, the command creates a new file of the specified size.
    For example, the following command extends the existing, smaller primary page file PAGEFILE.SYS:


    SYSGEN> CREATE PAGEFILE.SYS/SIZE=100000
    

    For more information about the SYSGEN command CREATE, refer to the SYSGEN section in the OpenVMS System Management Utilities Reference Manual.

    Note

    Frequent file creation and deletion can cause the free space on a disk to become severely fragmented. SYSGEN issues a HEADERFULL warning message if it determines that the creation or extension of a system file would cause that file to become fragmented enough to render the system unbootable. If this occurs, Compaq recommends that you back up and restore your system disk to consolidate the free space on the volume into one contiguous area. For more information, see Section 10.17.
    After you restore the disk, retry the SYSGEN operation. When SYSGEN issues a warning message, the file might be somewhat larger, but not as large as the value specified in the CREATE command.
  3. Use the following table to determine if you should reboot to use the new or modified file:
    Type Change Reboot Required?
    Primary page, swap, system dump, or error log dump file 1 New file Yes
      Extended file Yes
    Secondary page or swap file New file No 2
      Extended file Yes

    1Primary page, swap, and dump files are SYS$SPECIFIC:[SYSEXE] PAGEFILE.SYS, SWAPFILE.SYS, SYSDUMP.DMP; and SYS$ERRLOG.DMP.
    2Although rebooting the system is unnecessary, you must install secondary files before the system can use them. For more information, see Section 15.13.

  4. If you create a new version of the file, purge the old version after the system reboots.
  5. Add commands to the site-specific startup command procedure SYPAGSWPFILES.COM to make sure the files are installed each time the system boots. For instructions, see Section 15.13.
  6. If you do not want AUTOGEN to resize the files according to its calculations, edit MODPARAMS.DAT to specify the sizes of these files. Follow the instructions in Section 15.15.1.2.

Example

The commands in the following example extend the existing files PAGEFILE.SYS, SWAPFILE.SYS, and SYSDUMP.DMP to the specified sizes:


$ RUN SYS$SYSTEM:SYSGEN
SYSGEN> CREATE PAGEFILE.SYS/SIZE=100000
%SYSGEN-I-EXTENDED, SYS$SYSROOT:[SYSEXE]PAGEFILE.SYS;1 extended
SYSGEN> CREATE SWAPFILE.SYS/SIZE=30000
%SYSGEN-I-EXTENDED, SYS$SYSROOT:[SYSEXE]SWAPFILE.SYS;1 extended
SYSGEN> CREATE SYSDUMP.DMP/SIZE=33000
%SYSGEN-I-EXTENDED, SYS$SYSROOT:[SYSEXE]SYSDUMP.DMP;1 extended
SYSGEN> EXIT   


Chapter 16
Performance Considerations

This chapter introduces the basic concepts of performance management. For more detailed information, refer to OpenVMS Performance Management.

Information Provided in This Chapter

This chapter describes the following tasks:
Task Section
Knowing your work load Section 16.2
Choosing a work load management strategy Section 16.3
Distributing the work load Section 16.4
Predicting when tuning is required Section 16.6
Evaluating tuning success Section 16.7
Choosing performance options Section 16.8
Installing images with the Install utility (INSTALL) Section 16.9

This chapter explains the following concepts:
Concept Section
Performance management Section 16.1
System tuning Section 16.5
Images and known images Section 16.9.1
Known file lists Section 16.9.2
Attributes of known images Section 16.9.3

16.1 Understanding Performance Management

Performance management means optimizing your hardware and software resources for the current work load. This task entails several distinct but related activities:

16.2 Knowing Your Work Load

One of the most important assets that a system manager brings to any performance evaluation is an understanding of the normal work load and behavior of the system. Each system manager must assume the responsibility for understanding the system's work load sufficiently to be able to recognize normal and abnormal behavior; to predict the effects of changes in applications, operations, or usage; and to recognize typical throughput rates. The system manager should be able to answer such questions as the following ones:

If you are new to the OpenVMS operating system or to system management, you should observe system operation using the following tools:

The OpenVMS Performance Management provides detailed procedures for using the Monitor utility and, to a lesser extent, other operating system tools to observe and evaluate system performance. Also, the OpenVMS System Management Utilities Reference Manual provides reference information about using the Monitor utility.

Over time you will learn about metrics such as the typical page fault rate for your system, the typical CPU usage, the normal memory usage, and typical modes of operation. You will begin to see how certain activities affect system performance and how the number of users or the time of day affects some of the values.

As you continue to monitor your system, you will come to know what range of values is acceptable, and you will be better prepared to use these same tools, together with your knowledge, to detect unusual conditions. Routine evaluation of the system is critical for effective performance management. The best way to avoid problems is to anticipate them; you should not wait for problems to develop before you learn how the system performs.

You can learn more about your system's operation if you use the Monitor and Accounting utilities on a regular basis to capture and analyze certain key data items. By observing and collecting this data, you will also be able to see usage trends and predict when your system may reach its capacity.

You should also understand that system resources are used by system management tools. Be careful, therefore, in selecting the items you want to measure and the frequency with which you collect the data. If you use the tools excessively, the consumption of system resources to collect, store, and analyze the data can distort your picture of the system's work load and capacity. The best approach is to have a plan for collecting and analyzing the data.

16.3 Choosing a Work Load Management Strategy

System performance is directly proportional to the efficiency of work load management. Each installation must develop its own strategy for work load management. Before adjusting any system values, make sure you resolve the following issues:

16.4 Distributing the Work Load

You should distribute the work load as evenly as possible over the time your system is running. Although the work schedule for your site may make it difficult to schedule interactive users at optimum times, the following techniques may be helpful:

16.5 Understanding System Tuning

Tuning is the process of altering various system values to improve overall performance possible from any given configuration and work load. However, the process does not include the acquisition and installation of additional memory or devices, although in many cases such additions (when made at the appropriate time) can vastly improve system operation and performance.

On most systems, the work load is constantly changing. System parameters that produce optimal performance at one time may not produce optimal performance a short time later as the work load changes. Your goal is to establish values that produce acceptable performance under all of the changing work load conditions.

Before you undertake any action, you must recognize that the following sources of performance problems cannot be cured by adjusting system values:

When you make adjustments, you normally select a very small number of values for change, based on a careful analysis of the behavior you observed. You control system resources by tuning the values of two types of parameters:
Parameter Type Description
System parameters The values set for system parameters control system resources on a systemwide basis. The AUTOGEN command procedure automatically sets system parameters to appropriate values for your system configuration. AUTOGEN can also record feedback from a running system to adjust those parameters based on the system's work load.

The OpenVMS Performance Management describes how to select the parameters and new values that are likely to produce the desired changes.

Section 14.5 explains how to use AUTOGEN to modify system parameter values.

UAF limits and quotas The values set for limits and quotas in each user authorization file (UAF) record control system resources on a per-user basis. To control these values, use the Authorize utility. For information, see Section 6.11.

Before you undertake any tuning operation, be sure you are familiar with the resource management mechanisms described in the OpenVMS Performance Management. Understand the nature of system values before adjusting them. Without the proper level of understanding, you might degrade, rather than improve, overall performance.

16.6 Predicting When Tuning Is Required

Under most conditions, tuning is rarely required for OpenVMS systems. The AUTOGEN command procedure, which is included in the operating system, establishes initial values for all the configuration-dependent system parameters so that they match your particular configuration. For information about AUTOGEN, see Section 14.4.

Additionally, the system includes features that, in a limited way, permit it to adjust itself dynamically during operation. That is, the system detects the need for adjustment in certain areas, such as the nonpaged dynamic pool, the working set size, and the number of pages on the free and modified page lists. The system makes rough adjustments in these areas automatically. As a result, these areas can grow dynamically, as appropriate, during normal operation.

Experience has shown that the most common cause of disappointment in system performance is insufficient hardware capacity. Once the demand on a system exceeds its capacity, adjusting system values will not result in any significant improvements, simply because such adjustments are a means of trading off or juggling existing resources.

Although tuning is rarely required, you should recognize that system tuning may be needed under the following conditions:

16.7 Evaluating Tuning Success

Whenever you adjust your system, you should monitor its behavior afterward to be sure that you have obtained the desired results. To observe results, use the Monitor utility and the various forms of the DCL command SHOW. Refer to the OpenVMS DCL Dictionary for detailed information about the SHOW command. See Section 18.8.2 for information about using MONITOR. Refer to the OpenVMS System Management Utilities Reference Manual for detailed descriptions of MONITOR commands.

For example, you might consider running some programs (whose results you believe are fixed and reproducible) at the same time that you run your normal work load. If you run the programs and measure their running times under nearly identical work load conditions both before and after your adjustments, you can obtain a basis for comparison.

However, when applying this technique, remember to take the measurements under very similar work load conditions. Also, remember that this test alone does not provide conclusive proof of success. The possibility always exists that your adjustments may have favored the performance of the image you are measuring---to the detriment of other images. Therefore, in all cases, continue to observe system behavior closely for a time after you make any changes.

16.8 Choosing Performance Options

The following list of optional system management operations, normally performed after installation, often result in improved overall performance. Choose the options that are appropriate for your site. Not all options are appropriate at every site.


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