How to know if the IDMS programs pools are properly sized

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Article ID: 128493

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Updated On:

Products

CA IDMS CA IDMS - Database CA IDMS - ADS

Issue/Introduction



How can we tell if our IDMS Program and Reentrant Pools are optimally sized?

Environment

Release: IDADSO00200-19.0-ADS-for CA-IDMS
Component:

Resolution

To get size and load statistics, a list of the programs in the pool and pool map for a particular program pool you can use the 
DCMT D ACTIVE  PROGRAMS  command in one of four formats:

DCMT D ACTIVE PROGRAMS will display this info for the 24-bit non-reentrant Program Pool
DCMT D ACTIVE REENTRANT PROGRAMS will display this info for the 24-bit Reentrant Pool
DCMT D ACTIVE XA PROGRAMS will display this info for the 31-bit non-reentrant Program Pool
DCMT D ACTIVE XA REENTRANT PROGRAMS will display this info for the 31-bit Reentrant Pool

An example of the stats displayed:

***  Display of XA Reentrant Pool  ***                          
                       Pages in pool     34936                  
                       Bytes in pool  17887232                  
                       Loads to pool       191                  
                        Pages loaded     25505                  
                      Load conflicts         0                  
                                                                
                 CURRENT ALLOCATIONS                            
                     Pages allocated     25505  73% of pool     
         Pages in use by one program       204   1% of pool     
   Pages in use by multiple programs         0   0% of pool     
  High-Water mark of pages allocated     25505  73% of pool     
        Loads into unallocated space       191 100% of loads    
 Loads overlaying program not in use         0   0% of loads    
     Loads overlaying program in use         0   0% of loads    


An optimally sized pool is one that is large enough that All of the programs that CAN be loaded into the pool can fit at the same time.

The two most important statistics that will indicate if the pool is large enough are the last two

 Loads overlaying program not in use         0   0% of loads    
     Loads overlaying program in use         0   0% of loads  


  These stats should always be 0.
  The Loads overlaying programs in use will most likely always show 0,  But the Loads overlaying programs Not in use may be non zero and this is an indication that the pool is not large enough.
   When a request to load a program into a program pool occurs, IDMS will first look for contiguous UNUSED space in the pool large enough to fit the program. 
   If there is not sufficient Unused space, IDMS will find programs not currently in use and use that space to load the new program, marking the overlaid programs as such so that if they are called at a later time they would need to be Re-loaded into the pool.   
   If you can make your program pools  large enough so that no programs ever need to be overlaid to fit a new program load, that is optimal.