Re: Heap space size

[Tim Bronski <tim.bronski@xxxxxxxxx>]

I have a customer that's getting an out-of-memory error on a realloc. 
The size requested is only about 800k so it's unusual. What limits the 
default heap memory available to an activation group?

On 7/30/2019 3:16 AM, Mark Waterbury wrote:
>   Not sure exactly what you may be after, or trying to control, etc. -- but a good place to start is to look at the MI instructions pertaining to the heap:
>      ALCHS    Allocate Heap Space
>      CRTHS    Create Heap Space    etc.
>
> Start here:
> https://www.ibm.com/support/knowledgecenter/en/ssw_ibm_i_73/rzatk/topics.htm#topics__heapman
>     
>
> Each ILE activation group (including the default activation group, as a special case, for OPM programs), gets its own associated ILE heap space.   But, you can also use the CRTHS MI instruction (or the equivalent ILE built-in function) to do this yourself, thus creating additional heaps that you want to manage yourself.
>
> Study the CRTHS instruction to see all of the various "attributes" of these heaps that you can control.
>
> See also the ILE Concepts manual, here:
> https://www.ibm.com/support/knowledgecenter/ssw_ibm_i_73/ilec/sc415606.pdf
>
> Chapter 10. Storage management.
>
>
> Chapter 10 talks about the CEE APIs for Heap Space management.  Most of them are almost a one-to-one mapping on top of the above mentioned MI instructions.   So, from any ILE higher-level compiled language, you can use those APIs directly to manipulate the ILE heap(s).
>
>
> By the way, if you ever code %ALLOC or the ALLOC opcode in ILE RPG IV, you are in fact using CEEGTST.
>
> Page 123 of the above manual talks about various attributes for "tuning" and controlling the ILE heap spaces.
>
> Also, for the best possible performance, never do a "dispose" -- just do new, new, new, or alloc, alloc, alloc, and then, destroy (delete) the entire heap space when you are done with "all that stuff."   There is a flag that gets set the first time you do a "dispose" or "free" of storage in each ILE heap, and once that flag is set on, every call to alloc, free, etc. for that heap space, incurs additional storage accounting "overhead".
>
>
> Does that help?
>
> Mark S. Waterbury
>
>      On Monday, July 29, 2019, 6:18:23 PM EDT, Tim Bronski <tim.bronski@xxxxxxxxx> wrote:
>   
>   What are the all parameters that control an activation group's heap
> space size?