VSAM data trap

CAUTION:

The VSAM data trap described in this topic is intended to be used under the direction of IBM Service. It can cause performance degradation due to the additional validation of data records before they are written to DASD. You should enable the VSAM data trap only after contacting IBM service when a problem is encountered related to a data CI and additional diagnostic data is needed for problem determination. The VSAM data trap should be disabled as soon as the data is collected.

If the data component of a key-sequenced data set (KSDS) is damaged, the problem may show up in several ways, including:

Records out of sequence
Records in the freespace area
Problems with RDF or CIDF fields.

If data corruption occurs, the VSAM data trap can help to:

Prevent the record from being added incorrectly
Collect documentation close to the time of the problem. Without the VSAM data trap, diagnostic data is collected too long after the initial error and is usually not sufficient to diagnose the problem.

The VSAM KSDS data trap includes the following features and limitations. It:

Is only for KSDS
Does not test spanned records or when there can be only one record in a CI
Cannot test for sequence errors between control intervals
Tests key sequence in the CI as it is being written to DASD
Examines the Control Interval (CI) to see if the keys have correct value as related to the keys for the previous, and next, control interval (CI).

Use the following MVS commands to turn the data trap off or on. By default, the VSAM data trap is off.

Make VSAM data components eligible for the data trap:
```
V SMS,MONDS(IGWVSAM.BASE.DATA.TRAP),ON[,](data component name1,…,data component name8) 
```
At least one data component name must be provided. The following additional syntax rules apply.
- The maximum length for the entire data set mask is 44 characters.
- An asterisk (*) or percent sign (%) can be specified anywhere except in the first position.
- % represents any single character. For example, %%% represents any 3 characters.
- * by itself indicates that at least one qualifier occupies that position. * within a qualifier represents zero or more characters.
- A qualifier can be a single *.
- ** represents zero or more qualifiers.
- ** cannot appear with any other characters within a qualifier.
- Three or more adjacent asterisks (for example, ***) are not allowed within a qualifier.
The data components are enabled when they are opened. To add more data components to the list, issue the command with new data component names. The data set specified in the command is enabled to use the data trap, and any data set previously enabled for the data trap is enabled again and remains eligible until the data set is closed.
To make all VSAM data components eligible for the data trap, use an asterisk in place of the data component names, as follows:
```
V SMS,MONDS(IGWVSAM.BASE.DATA.TRAP),ON(*)
```
Turn the data trap off for future use:
```
V SMS,MONDS(IGWVSAM.BASE.DATA.TRAP),OFF
```
To disable the data trap for any existing data set being trapped, the data set must be closed.
To determine if the data trap is active for the system:
```
D SMS,MONDS(IGWVSAM.BASE.VSAM.DEBUG.FEATURES)
```
This displays the status of VSAM diagnostic features. If the data trap is enabled, the command displays the data component name(s) found in the current data trap list created when you last enabled the data trap with the VARY SMS command. Any data set previously enabled for the data trap remains eligible until the data set is closed.