DC084116 WAITING FOR FREE RPL how to calculate the RPL count

Products

• IDMS
• IDMS - Database

Issue/Introduction

Getting message in IDMS:

DC084116 Vnnn LOGICAL UNIT <ple-name>(<lu-name>) WAITING FOR FREE RPL

What is an RPL and what is the best way to calculate the RPL count for an IDMS VTAM line? 

Environment

Release: 19.0

Cause

From the DC084116  message description:

Reason:

The indicated logical unit is waiting for a free RPL. This message is issued at the first and every 100th occurrence. The number of RPL waits should ideally be kept to zero. A large number of waits can lead to instabilities and poor performance.

An RPL is a control block used to communicate with VTAM. An RPL is required each time a read or write request is issued to VTAM.
You specify the number of RPLs in the LINE statement of the IDMS SYSGEN. The number of RPLs determine the number of terminal requests that can be handled concurrently by the VTAM line.

The RPL is allocated for the duration of the terminal I/O then it is released and can be used by another terminal. If there are insufficient RPLs defined, a terminal has to wait for another request to complete and an RPL to become available. This can result in degraded response times on the line.

The DC084116 message indicates there are insufficient RPLs defined for the VTAM line.

Resolution

The number of RPLs to define depends on the type of VTAM line:

• For lines defined in the SYSGEN as TYPE is VTAMLIN the recommended number of RPLs is 20 percent of the number of terminals defined in the line, plus one for each printer defined.
  
  
• For lines defined in the SYSGEN as TYPE is VTAMLU (LU6.2 terminals) you need to define sufficient RPLs to handle the maximum number of concurrent I/O requests on the line. If unsure of the number of concurrent sessions increase the number of RPLs and monitor for any RPL waits on the line.

You can monitor RPL usage using the realtime performance monitor. Use task code PMRM and press PF3 - Communication Line Detail.
Look at the Waits On RPL column. You want the waits on RPL count to be 0 or close to it. If you see a high number of waits it means you need to increase the number of RPLs.

To modify the number of RPLs use the SYSGEN compiler and the following syntax:

MOD SYSTEM <version-number>.
MOD LINE <line-name> RPL <rpl-count>.
GENERATE.

 

Additional Information

See IDMS documentation sections VTAMLIN Parameters and VTAMLU Parameters.