z/OS operating system tuning tips

There are several configuration changes you can make to z/OS® system components that might improve product performance.

You might want to make one or more of the following changes to the indicated z/OS components:

CTRACE
The first place to review is your CTRACE configuration. Ensure that all components are either set to MIN or OFF. To display the CTRACE options for all components on your system, issue the following command from the operator console:
```
D TRACE,COMP=ALL
```
To change the setting for an individual component to its minimum tracing value, use the following command, where xxx is the component ID.
```
TRACE CT,OFF,COMP=xxx
```
This configuration change eliminates the unnecessary overhead of collecting trace information that is not needed. Often during debug, CTRACE is turned on for a component and not shut off when the problem is resolved.
SMF
Ensure that you are not collecting more SMF data than you need. Review the SMFPRMxx settings to ensure that only the minimum number of records are collected.
Use SMF 92 or 120 only for diagnostics.
- SMF Type 92
  SMF Type 92 records are created each time an HFS file is opened, closed, deleted, and so forth. Almost every web server request references HFS files, so thousands of SMF Type 92 records are created. Unless you specifically need this information, turn off SMF Type 92 records. In the following example, we have disabled the collection of SMF type 92 records:
  Example:
```
 ACTIVE,  
 DSNAME(SYS1.&.SYSNAME..SMF.MAN1;SYS1.&SYSNAME..SMF.MAN2;),          
 NOPROMPT,   
 REC(PERM),   
 MAXDORM(3000),  
 STATUS(010000), 
 JWT(0510),     
 SID(&SYSNAME;(1:4)),  
 LISTDSN,           
 SYS(NOTYPE(19,40,92)),    
 INTVAL(30), 
 SYNCVAL(00),  
 SYS(DETAIL,INTERVAL(SMF,SYNC)),   
 SYS(EXITS(IEFACTRT,IEFUJI,IEFU29,IEFU83,IEFU84,IEFU85,IEFUJV,IEFUSI))
```
- SMF Type 120
  Best practice: You might find that running with SMF 120 records in production is appropriate, because these records give information specific to applications that are running on the product, such as response time for Enterprise Edition (Java EE) artifacts, bytes transferred, and so forth. If you do choose to run with SMF 120 records enabled, you should use server interval SMF records and container interval SMF records rather than server activity records and container activity records.
  To enable specific record types in the administrative console, specify the following properties:
  - server_SMF_server_activity_enabled=0 (or server_SMF_server_activity_enabled = false), which turns off SMF Subtype 1: Server activity record.
  - server_SMF_server_interval_enabled=1 (or server_SMF_server_interval_enabled = true), which turns on SMF Subtype 3: Server interval record.
  - server_SMF_container_activity_enabled=0 (or false), which turns off SMF Subtype 5: J2EE container activity record (Version 2).
  - server_SMF_container_interval_enabled=1 (or true), which turns on SMF Subtype 6: J2EE container interval record (Version 2).
  - server_SMF_request_activity_enabled=1 (or true), which turns on SMF Subtype 9: Request Activity record.
    Best practice: Because of the size of this record type, there is a performance impact when you are running this record. Therefore, when you run this record, you might want to turn off the collection of data for certain sections if you do not need that information. Turning off the collection of data for the sections that you do not need lessens the performance impact. See the description of the SMF 120 Type 9 record for more information on which sections can be turned off, and how to turn them off.
  - server_SMF_outbound_enabled (or true), which turns on SMF Subtype 10: Outbound Request records.
  - server_SMF_interval_length=1800.
You might also want to review your DB2® records and the standard RMF written SMF records, and ensure that the SMF data sets are allocated optimally. DB2 SMF records 100, 101 and 102 affect performance and should be used only for monitoring DB2 performance with the DB2 PM tool. If you are not monitoring DB2 performance, you should consider not collecting those SMF records.