2. PERFORMANCE REPORTING ANALYSIS › 2.5 Virtual Storage Management Analysis › 2.5.2 Usage Guidelines › 2.5.2.2 Major Impacts Upon Virtual Storage Usage

2.5.2.2 Major Impacts Upon Virtual Storage Usage

SYSTEM QUEUE AREA (SQA)

SQA size is specified at IPL via the member IEASYSnn in
SYS1.PARMLIB and does not change thereafter.  If it is
overspecified, virtual address space will be wasted.  If it
is underspecified, requests for unavailable SQA will be
satisfied from the CSA with little or no performance impact.

COMMON SYSTEM AREA (CSA)

Like SQA, CSA is specified at IPL via the member IEASYSnn and
does not change thereafter.  The size specified for CSA is
subtracted from the bottom PLPA address.  If this does not
end on a megabyte boundary, it is rounded down to the next
lower megabyte boundary to determine the top of the Private
Area.  Thus, small changes in the allocated size of CSA can
cause the Private Area to decrease by one megabyte if one of
these boundaries is crossed.

Major users of CSA are IMS, VTAM, and JES3.  A detailed
Knowledge of these subsystems and the parameters controlling
their generation and operation is necessary to assist in
managing their use of virtual storage.

PLPA, FLPA, AND MLPA

Analysis of virtual storage usage by the PLPA, FLPA, and MLPA
depends heavily upon detailed analysis of the modules found
in these areas.  You should be certain that non-IBM modules
which do not have to be in these areas for performance
reasons are excluded.  There should be periodic checking for
obsolete versions of system modules, such as the JES2 load
module HASPSSSM.  Searching for module names like HASPSSSX
and TSTXSSSM can aid in this sort of housecleaning.

PRIVATE AREA

The management of virtual storage in the Private Area depends
upon a detailed knowledge of the subsystem or application
under concern.  For instance, for JES2, specifying
inappropriate sizes for buffers can lead to wasted, unusable
space in the JES2 Private Area.