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Updated: 11 December 1998

OpenVMS Performance Management


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1.3.1 Prerequisites

Before you adjust any system parameters, you should:

1.3.2 System Utilities and Tools

You can observe system operation using the following tools:

On Alpha platforms, Compaq recommends using the DECevent utility instead of the Error Log utility, ANALYZE/ERROR_LOG. (You invoke the DECevent utility with the DCL command, DIAGNOSE.) You can use ANALYZE/ERROR_LOG on Alpha systems, but the DECevent utility provides more comprehensive reports.

1.3.3 Why Use Them?

These system utilities and tools allow you to:

1.3.4 Knowing Your Work Load

The experienced system manager can answer the following questions:

Note

If you are a novice system manager, you should spend a considerable amount of time observing system operation using the DCL commands ACCOUNTING, MONITOR, and SHOW.

1.4 Developing a Strategy

Each installation site must develop its own strategy for optimizing system performance. Such a strategy requires knowledge about system use in the following areas:

1.4.1 Managing the Work Load

Before you attempt to adjust any system values, always ask yourself the following questions:

1.4.2 Distributing the Work Load

Distribute the work load as evenly as possible using the following techniques:

1.4.3 Application Code Sharing

Application code sharing provides a cost-effective means of optimizing memory utilization. To ensure optimum performance of your system, make sure that frequently used code is shared.

Use the site-specific startup procedure to install as shared known images user-written programs and routines that are designed for sharing and have reached production status or are in general use.

Encourage programmers to write shareable code.

1.5 Analyzing Complaints

Typically, an investigation into system performance begins when you receive a complaint about a slowdown of interactive response times or about some other symptom of decreased throughput. Before you decide that the current complaint reflects a performance problem, you should:

1.5.1 Preliminary Steps

You will need some additional information as described in the following table:
Step Action
1 Obtain the following information:
  • Number of users on the system at the time the problem occurred
  • Number of jobs on the system
  • Response times
  • Evidence of jobs hanging and unable to complete
2 Compare these facts with your knowledge of the normal work load and operation of your system.
3 Follow the procedure shown in Figure A-1 to verify the validity of the complaint.
4 Did you observe the problem? Can you duplicate the problem?

1.5.2 Hardware Problem?

Hardware problems are a common source of performance complaints.
Step Action
1 Check the operator log and error log for indications of problems with specific devices.
2 Enter the DCL commands SHOW ERROR and ANALYZE/ERROR_LOG to help determine if hardware is contributing to a performance problem.
3 Review the previous day's error log as part of your morning routine.
4 Obtain a count of errors logged since yesterday. Use the following DCL command (which requires SYSPRV privilege):
 $ ANALYZE/ERROR_LOG/BRIEF/LOG/OUTPUT=DAILY.LOG/SINCE=YESTERDAY

For more information about error logging, see the OpenVMS System Manager's Manual: Tuning, Monitoring, and Complex Systems; for information about using the Analyze/Error_Log utility, refer to the OpenVMS System Management Utilities Reference Manual: A--L.

1.5.3 Blocked Process?

A process enters the miscellaneous resource wait (MWAIT or RWAST) state usually because some resource, such as paging file or mailbox, is unavailable (for example, because of low quota or a program bug).

To identify processes in the MWAIT state, use the DCL command MONITOR STATES.
If... Then...
a process is in the MWAIT state use the DCL commands MONITOR PROCESSES and SHOW SYSTEM to identify the reason for the MWAIT state.
the system fails to respond while you are investigating an MWAIT condition check the system console for error messages.
the MWAIT condition persists after you increase the capacity of the appropriate resource investigate the possibility of a programming design error.

1.5.4 Unrealistic Expectations?

Always bear in mind that what appears at first to be a performance problem can turn out to be a case of unrealistic expectations. For example:

Adjusting system values will accomplish nothing in such circumstances.

Note

Whenever you can anticipate a temporary workload change that will affect your users, you should notify them through broadcasts, text, or both, in the system notices.


Chapter 2
Performance Options

Generally, system performance problems are the result of poor operation, lack of understanding of the work load and its operational ramifications, lack of resources, poor application design, human error, or a combination of these factors.

System management operations, normally performed after installation, often result in improved overall performance. This chapter discusses the following topics:

Note that not all the options discussed in this chapter are appropriate at every site.

2.1 Decompressing System Libraries

Most of the OpenVMS libraries are in compressed format in order to conserve disk space.

The CPU dynamically decompresses the libraries whenever they are accessed. However, the resulting performance slowdown is especially noticeable during link operations and when requesting online help.

If you have sufficient disk space, decompressing the libraries will improve CPU and elapsed-time performance.

To decompress the libraries, invoke the command procedure SYS$UPDATE:LIBDECOMP.COM.

Note

Decompressed object libraries take up about 25 percent more disk space than when compressed; the decompressed help libraries take up about 50 percent more disk space.

2.2 Disabling File System High-Water Marking

High-water marking is set by default whenever a volume is initialized. This security feature guarantees that users cannot read data they have not written.

Disabling high-water marking improves performance when data is written past the current end-of-file. The amount of improvement depends on the following considerations:

To disable high-water marking, specify the /NOHIGHWATER_MARKING qualifier when initializing the volume, or do the following at any time:

  1. Enter a DCL command similar to the following:


    $ SET VOLUME/NOHIGHWATER_MARKING device-spec[:]
    

  2. Dismount and remount the volume.

2.3 Setting RMS File-Extend Parameters

Because files extend in increments of twice the multiblock count (default is 16), system defaults now provide file extensions of only 32 blocks. Thus, when files are created or extended, increased I/O can slow performance. The problem can be overcome by:

2.4 Installing Frequently Used Images

When an image is used concurrently by more than one process on a routine basis, install the image with the Install utility (INSTALL), specifying the /OPEN, /SHARED, and /HEADER_RESIDENT qualifiers. You will ensure that:

You may use either of the following commands:


INSTALL ADD/OPEN/SHARED/HEADER_RESIDENT filename
INSTALL CREATE/OPEN/SHARED/HEADER_RESIDENT filename

ADD and CREATE are synonyms. The /SHARED and /HEADER_RESIDENT qualifiers imply the image is open. The /OPEN qualifier indicates the file is a permanently known image to the system.

2.5 Enabling Virtual I/O Caching

Enable virtual I/O caching to reduce the number of disk I/O operations. (See Section 12.2.)

2.6 Reducing System Disk I/O

Remove frequently accessed files from the system disk and use logical names, or where necessary, use other pointers to access them as shown in the following table:
Logical Name File
ACCOUNTING System Accounting Data File
AUDIT_SERVER Audit server master file
QMAN$MASTER Job queue database master file 1
Directory specification 2 Job queue database queue and journal files
NETPROXY NETPROXY.DAT
OPC$LOGFILE_NAME Operator log files
RIGHTSLIST RIGHTSLIST.DAT
SYS$ERRORLOG ERRFMT log files
SYS$JOURNAL DECdtm transaction log files
SYS$MONITOR MONITOR log files
SYSUAF SYSUAF.DAT
VMSMAIL_PROFILE VMSMAIL_PROFILE.DATA


1Mount the disk on which it resides in SYLOGICALS.
2When used with the DCL command START/QUEUE/MANAGER.

In addition, the default DECNET account can reside on another disk. Refer to the DECNET record in the system authorization file.

You might consider moving paging and swapping activity off the system disk by creating large secondary page and swap files on a less heavily used disk.

In an educational or learning environment, there are several other files you might want to move off the system disk. If many users will frequent access the HELP libraries, the directory pointed to by logical name SYS$HELP could be moved to another disk. However, the system installation and upgrade procedures assume SYS$HELP is on the system disk. If you move SYS$HELP to another disk, you will have to update it manually after a system upgrade.

If computer-based instruction programs are frequently used, SYS$INSTRUCTION or DECW$CBI, or both can be moved off the system disk or made into search lists.

Similarly, if the system is often used for Bookreader documentation, DECW$BOOK can be located off the system disk, or the logical name can be implemented as a search list.

These changes should be made only if you have determined that the files in these directories are frequently used on your system.

2.7 Tuning

Tuning is the process of altering various system values to obtain the optimum overall performance possible from any given configuration and work load.

You will rarely need to make major adjustments to system parameters.

Note

When you have optimized your current system, the acquisition and installation of additional memory or devices can vastly improve system operation and performance.

Always aim for best overall performance, that is, performance viewed over time. The work load is constantly changing on most systems. Therefore, what guarantees optimal workload performance at one time might not produce optimal performance a short time later as the work load changes.

2.7.1 Prerequisites

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

2.7.2 Tuning Suggestions

Tuning is rarely required for OpenVMS systems for the following reasons:

Although tuning is rarely required, be aware that it is appropriate in response to two particular situations:

  1. If you have adjusted your system for optimal performance with current resources and then acquire new capacity, you must plan to compensate for the new configuration. In this situation, the first and most important action is to execute the AUTOGEN command procedure.
  2. If you anticipate a dramatic change in your workload, you should expect to compensate for the new workload.

2.7.3 Tools and Utilities

Using the AUTOGEN command procedure to manage your system parameters is recommended. If you modify a system parameter using AUTOGEN, AUTOGEN makes automatic adjustments in associated parameters. See the OpenVMS System Manager's Manual for a detailed description of the AUTOGEN command procedure.

Caution

Do not directly modify system parameters using SYSGEN. AUTOGEN overrides system parameters set with SYSGEN, which can cause a setting to be lost months or years after it was made.

Use AUTHORIZE to change user account information, quotas, and privileges.

2.7.4 When to Use AUTOGEN

Run AUTOGEN in the following circumstances:

AUTOGEN will not fix a resource limitation.

2.7.5 Adjusting System Parameter Values

When it becomes necessary to make adjustments, you normally select a very small number of values for change, based on a careful analysis of the behavior observed. These values are usually either system parameters or entries in the user authorization file (UAF).
If you want to... Then...
modify system parameters use the AUTOGEN command procedure.
change entries in the UAF use AUTHORIZE.


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