Controlling data set recording

You control the recording of samples to the VSAM data sets through the data gatherer option DATASET. The syntax is:


   .-DATASET(STOP,NOSWITCH)------.   
>>-+-----------------------------+-----------------------------><
   |     .-,-----------------.   |   
   |     V                   |   |   
   '-DS(-----| Suboption |---+-)-'   

Suboption

|--+---+--------------------------+---+-------------------------|
   |   |      .-,-------------.   |   |   
   |   |      V               |   |   |   
   |   +-ADD(---data-set-name-+-)-+   |   
   |   |      .-,-------------.   |   |   
   |   |      V               |   |   |   
   |   '-DEL(---data-set-name-+-)-'   |   
   |                                  |   
   +---START--------------------------+   
   +---SWITCH-------------------------+   
   |        .-(7)-----.               |   
   '-WHOLD--+---------+---------------'   
            '-(value)-'

Specify at least one of the following suboptions:

ADD|DEL
START|STOP
SWITCH|NOSWITCH
WHOLD

ADD(data-set-name[,data-set-name])|DEL(data-set-name[,data-set-name])

Allows you to specify the name of the data set on which you want RMF™ to start or stop recording data. The name must match the name in the DEFINE CLUSTER statement. If you use a name that has not been defined, RMF issues a message.

ADD(data-set-name) allows RMF to use the specified data set to record sampled data. DEL(data-set-name) removes the specified data set from the list of data sets RMF uses to record data.

When you specify more than one data set name:

Use a comma as a separator
Specify no more than 100 data sets. If you specify more, RMF issues an error message
Ensure that each data set name is unique

Examples:

To specify two data sets for data set recording, use the following option:
```
DATASET(ADD(RMF.DS01))
DATASET(ADD(RMF.DS02))
```
RMF uses the empty data sets in the order in which they are defined. During data set recording, RMF writes the samples from its local storage buffer to the data sets. When all the data sets are full, RMF reuses the data sets, starting with the one that contains the oldest data.
If you want to save data already recorded on a data set and make sure RMF does not reuse it, use the suboption DEL. This prevents RMF from writing over data in the specified data set. To save data contained in RMF.DS01, specified in the previous example, specify:
```
DATASET(DEL(RMF.DS01))
```
RMF does not reuse the data set during data set recording.

START|STOP

Allows you to start or stop data set recording. You can issue START|STOP at the beginning of a session on the session command START, or while the data gatherer is active with the session command MODIFY. If you do not want data set support for the data gatherer, use the default, which is DATASET(STOP).

RMF handles the START|STOP suboptions only at the end of a MINTIME. At this point, RMF has collected a set of samples representing the smallest sample time that the data reporter can display on the screen. By waiting until the end of the MINTIME to handle the START|STOP suboptions, RMF avoids recording partial sets of samples in the data sets.

SWITCH|NOSWITCH

Controls RMF's selection of a data set for recording sampled data.

If you specify SWITCH, RMF chooses the active data set as follows:

RMF searches for an empty data set to record samples
If there are no empty data sets, RMF reuses the data set with the oldest data

This option lets you reuse the specified data sets continuously, overlaying the oldest data once all the data sets are full.

If you specify NOSWITCH, or omit this suboption, RMF chooses the active data set as follows:

RMF searches for the data set with the most recent data and records samples if the data set is not full
If the data set with the most recent data is full, RMF searches for an empty data set to record samples
If there are no empty data sets, RMF reuses the data set with the oldest data

This option allows you to start the data gatherer and continue writing samples on a currently active data set that still has free space.

Note: NOSWITCH is effective only if specified or defaulted to when you start the data gatherer. It has no effect when specified on the session command MODIFY.

WHOLD(value)

Allows you to specify, in megabytes, a storage value that controls page releases in the RMF local storage buffer. The valid range of values for WHOLD is 1 to 999. RMF uses a default of 7 if you do not specify a value. If you specify a value outside the valid range, RMF uses 999 megabytes for a value above the range and 1 megabyte for a value below the range.

A page release discards the current and former copies of a page that are on central, expanded, or auxiliary storage, so that the page will not be read in before it is reused for new data. When the data in the local storage buffer has been copied to the data set and the storage amount exceeds the WHOLD value, the storage with duplicate data in the buffer becomes eligible for page release.

WHOLD works with the WSTOR option (see WSTOR) to control the page space needed for the storage buffer. You can specify a WHOLD value independent of the WSTOR value. If WHOLD is smaller than WSTOR:

Page releases can occur before RMF uses all the storage in the local storage buffer
When you turn data set recording off, the local storage buffer size assumes the WSTOR value.

If WHOLD is equal to or greater than WSTOR:

Page releases occur once the WSTOR value is exceeded and RMF begins to wrap around the buffer.

When you activate data set recording, and the buffer contains data that the gatherer has already copied to the data set, the local storage buffer size reverts to the WHOLD value.