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Reserved Memory "Fragmentation"

 
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Jack Trachtman
Super Advisor

Reserved Memory "Fragmentation"

Is it possible for Reserved Memory to become fragmented?

I've heard people say this, but my picture of RM is that it is a permanently assigned contiguous section of memory allocated during boot (along with the tables to map to it) and so it wouldn't be able to get "fragmented".

Over the years I've seen a few of our DB products which use RM that, when we try to restart them, for unclear reasons cannot re-access the RM that they had just been using!

What could cause this?

Could there be an issue with the page tables that VMS assigns to the RM not being accessible for some reason after we restart these apps?

TIA
6 REPLIES
Richard J Maher
Trusted Contributor

Re: Reserved Memory "Fragmentation"

Hi Jack,

I never heard of the issues you describe; maybe if you have a specific example someone could help? I'd recommend shared page tables where possible.

And for those who don't know, Oracle Rdb with now be able to use the Reserved Memory Registry for Global Buffers! (I believe Orrible Oracle has been doing this for about 5 years on VMS)

Attached is an example of home grown RM use if it helps.

Regards Richard Maher
Richard J Maher
Trusted Contributor

Re: Reserved Memory "Fragmentation"

And here's the second part of the example.
Tom O'Toole
Respected Contributor
Solution

Re: Reserved Memory "Fragmentation"


Jack, during your restart, are you sure the memory is getting completely released by the app prior to the restart? Can you put a show memory in there between the shutdown and restart?
Can you imagine if we used PCs to manage our enterprise systems? ... oops.
Ian Miller.
Honored Contributor

Re: Reserved Memory "Fragmentation"

Did you use the /PAGE_TABLES qualifier when creating the reserved memory. What does
SYSMAN RESERVED_MEM SHOW
say about your reserved memory area?
____________________
Purely Personal Opinion
Jack Trachtman
Super Advisor

Re: Reserved Memory "Fragmentation"

We were able to test our application and found that in shutting it down it actually did not release Reserved Memory! (We have now learned that the product "sometimes" does this!)

Richard J Maher
Trusted Contributor

Re: Reserved Memory "Fragmentation"

Hi Jack,

So what? Data persistance is a good thing!

This is what Rdb should be doing and isn't :-(

If you reserve 16MB of physical memory for you Global Buffers and it takes N interval to fully populate that memory then I, for one, would like the data to persist and remain available for re-mapping when traversing database closure.

Obviously if the meta-data changed or the Global Section should be voided the the version number would sort that out.

Once again, "What is the *exact* problem?" and "What are you trying to do *exactly*?" might help. Software product names and versions would help or would that identify your client?

This link may help: -
http://h71000.www7.hp.com/doc/82FINAL/5841/5841pro_contents_005.html#toc_chapter_16

Also look at the pertinent examples I posted in the earlier replies. If you can't understand them then you need to retain the services of someone who can. And how is the weather in Bangalore anyway?

If you don't want the old data then delete the global section and make sure your dzero /zero and whatever else zero options are set.

Regards Richard Maher