AUTOGEN Performance Monitoring

The primary tuning program is automated in a script called SYS$UPDATE:AUTOGEN. It is fully described in the OpenVMS System Manager's Manual and the OpenVMS System Management Utilities Reference Manual. AUTOGEN is run automatically when OpenVMS is installed or upgraded, and nearly 100 system parameters are affected. This is necessary to optimize the various system tables and buffer sizes to the specific hardware configuration. The resulting system is tuned to the hardware but not to the user load. The system manager should manually run AUTOGEN in the feedback mode whenever the system hardware or software changes or when the workload changes.

The second use of AUTOGEN is to adjust for performance under load. Compaq/HP recommends that the AUTOGEN feedback option (which gathers performance data but makes no changes) be used weekly to monitor OpenVMS performance under actual running conditions. When run this way, key performance data gathered continuously by OpenVMS can be analyzed by AUTOGEN, which then recommends changes via a report. The report should be analyzed by the manager, who determines whether the system parameters should be changed. AUTOGEN can modify about 25 key system parameters based on peak system load.

Feedback data is collected with the command, and information is stored in SYS$SYSTEM:AGEN$FEEDBACK.DAT. It will be processed at a later time.

     $ @SYS$UPDATE:AUTOGEN SAVPARAMS SAVPARAMS FEEDBACK 

Later, when it is convenient, the system manager runs AUTOGEN again using that previously collected feedback data to determine possible changes to OpenVMS parameters. This is done with the following command:

     $ @SYS$UPDATE:AUTOGEN GETDATA TESTFILES FEEDBACK 

AUTOGEN then reports what the new parameter values should be in a file called SYS$SYSTEM:AGEN$PARAMS.REPORT. The report resembles the following:

     SYS$SYSTEM? type agen$params.report     AUTOGEN Parameter Calculation Report on node: BEAVER       This information was generated at 26-AUG-2002 10:45:31.75       AUTOGEN was run from GETDATA to TESTFILES using FEEDBACK     ** No changes will be done by AUTOGEN **        The values given in this report are what AUTOGEN would         have set the parameters to.     Processing Parameter Data files     -------------------------------     Including parameters from: SYS$SYSTEM:MODPARAMS.DAT     Including parameters from:  SYS$MANAGER:AGEN$NEW_NODE_DEFAULTS.DAT     Feedback information was collected on 26-AUG-2002 00:05:25.03       Old values below are the parameter values at the time of collection.       The feedback data is based on 499 hours of up time.       Feedback information will be used in the subsequent calculations     Parameter information follows:     ------------------------------     MAXPROCESSCNT parameter information:             Feedback information.                Old value was 110, New value is 90                Maximum Observed Processes: 46     GBLPAGFIL parameter information:             Override Information - parameter calculation has been overridden.                The calculated value was 1024.  The new value is 51024.                GBLPAGFIL has been increased by 50000.                GBLPAGFIL is not allowed to be less than 10000.     GBLPAGES parameter information:             Feedback information.                Old value was 156354, New value is 496878                Peak used GBLPAGES: 65456                Global buffer requirements: 51024             Override Information - parameter calculation has been overridden.                The calculated value was 129600. The new value is 496878.                GBLPAGES has been increased by 367278.                GBLPAGES is not allowed to be less than 62000. 

Once the manager reviews the changes and deems them necessary, AUTOGEN is run a third time (using the same feedback data) to make the changes to xVMSSYS.PAR. ^[1] This necessarily involves rebooting the system, and the command is:

     $ @SYS$UPDATE:AUTOGEN GETDATA REBOOT FEEDBACK 

Automated feedback data collection should be done daily and tuning perhaps weekly or whenever the system load changes. Because tuning (not feedback collection or analysis) requires rebooting, the system manager will have to carefully schedule this operation. AUTOGEN adjusts variables (some are interdependent) that control CPU, memory, and I/O performance. This data is stored in xVMSSYS.PAR so it is not lost after a boot. This file acts like the Windows NT Registry.

Manual tuning is done using the SYSMAN PARAMETER command, but a novice to OpenVMS internals should not attempt this task, because several hundred variables in xVMSSYS.PAR are quite complicated, and many of them depend on one another. Rather than using SYSMAN, the best management policy is to enter changes in MODPARAMS.DAT so AUTOGEN respects them when it runs. Thus, MODPARAMS.DAT serves as a documented history of changes to system parameters.

Variables other than those that control OpenVMS performance are stored in xVMSSYS.PAR. For instance, seven variables control login characteristics, such as how many unsuccessful login attempts are permitted, how long to inhibit login to an account after unsuccessful login, and the minimum number of characters in a password. SYSGEN PARAMETER is used to change this class of parameters. This topic is further discussed in Chapter 8.

^[1]Actually VAXVMSSYS.PAR on VAX machines and ALPHAVMSSYS.PAR on Alpha machines.