Datacom MRDF COVERED option FIRST/ACTIVE

Products

• Datacom
• DATACOM - AD
• Datacom/AD
• Datacom/DB

Issue/Introduction

How can you determine what areas should be defined as Memory Resident Data Facility (MRDF) COVERED and what COVERED option to specify, FIRST or ACTIVE?

The Memory Resident Data Facility allows areas to be defined as COVERED to keep data blocks resident in memory. This reduces the amount of physical read I/Os to that area and increases response time as there is less time spent in doing physical I/O which in turn reduces CPU usage.

Environment

Release: 15.1

Resolution

Candidate areas to be defined as COVERED are areas with the highest read count. Out of these areas then select the ones that belong to critical applications or applications that have poor performance. There are SQL queries in Article 55147 to help determine which areas will benefit most from being covered in terms of the I/O saved.

Another consideration is how much 64 bit storage is available and how much can be allocated to COVERED areas.

The COVERED FIRST option uses less memory and CPU because it is easier to manage but is only useful if the first part of the area is accessed the most.

The COVERED ACTIVE option would be better specially if only a small portion of the area is COVERED.

If you don't know how the area is used then start by allocating a portion of the area to COVERED ACTIVE and then look at the MRDF statistics to see if any benefit has been gained and adjust accordingly. Again use the SQL queries in Article 55147 to see the MRDF statistics. This is the normal procedure you would follow with any tuning exercise.

Additional Information

Datacom documentation section  COVERED FIRST and COVERED ACTIVE

Article 55147 - How do I determine which data/index areas are the best candidates to be implemented as covered