>I was going to say "deprecated" (I trust Skip to correct me if 
>the usage is incorrect :)  MLPA is still supported, but DLPA 
>is greatly preferred.

I disagree. Each has its place, as does PLPA and FLPA. 

If it is true that there is not enough (E)CSA available to accommodate the 
new copy of the load module, then yes an IPL is required.
Otherwise the module could be added to dynamic LPA. Whether that has any 
effect or not depends on the application that is referencing the module. 
If you can get the application to ask the system for the address of the 
module (and the application then uses that address), the system will 
return the address of the newly loaded copy and things will likely proceed 
fine. For a lot of applications stop/restart of that application will do 
that; but not for all.

It is true that if something has been loaded into dynamic LPA that you 
could delete it and the storage would be freed. But you'd better be 100% 
sure that no code is actually running within that storage area (and that 
is not something that can typically be done with existing programming 
interfaces, you would have to look at just about every stashed PSW in 
every system control block).  Thus deleting from dynamic LPA is not 
something to be done lightly, especially on a production system. If you 
get it wrong, then if you're lucky something blows up; if you're not lucky 
then you have introduced a system integrity exposure because there is no 
way of knowing what code is now being executed at the spot where a PSW 
happened to point.. 

Aside from the "delete" possibility, putting things into PLPA, MLPA, FLPA 
is better for the system than putting it into DLPA. For example, the 
system is able to pack all PLPA modules together so storage usage is more 
efficient.  Of course if you have a program object (in a PDSE) DLPA is 
your only choice.

Peter Relson
z/OS Core Technology Design


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