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?
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 KB000055147 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 KB000055147 to see the MRDF statistics. This is the normal procedure you would follow with any tuning exercise.
DocOps section COVERED FIRST and COVERED ACTIVE
KB000055147 - How do I determine which data/index areas are the best candidates to be implemented as covered
Video Performance Tuning in the ‘real world’ Part 1 , the COVERED part is around minute 34.
PDF for Performance Tuning in the ‘real world’ Part 1