[GAP Forum] How much memory is needed?

[Stephen Linton]

Hi Mark,

I can confirm that GAP will run successfully on a computer of that size. 
We have a couple of 512GB RAM machines and I've used all of that in some single GAP computations.
You may need to use some non-standard options at compile time or run time to get this to work though -- we can advise you at the time if necessary.

I have a few caveats though:

1. Not all the algorithms in GAP and the software it uses through packages, like ACE and KBMAG
are really "tuned" for this much data, so you may run into things that slow down more than they need to. Again, we may be able to advise or assist.

2. Most machines with this much memory have what is called a NUMA architecture -- the memory is divided between the processors and  they are not really designed for one processor to access all the memory in a random way. This may mean things suddenly slowing down by a factor of two or three when you use more than about 25% of your memory.

3. In my, entirely unsystematic, experience, there are not THAT many problems that can  be solved in 512GB that cannot be solved in 128. There will be some, but unless you have a predictable need for the memory, to hold matrices or something, there may not be so many.  Of course your mileage may vary.

	Steve

On 1 Oct 2013, at 14:08, Mark Sapir <markvs at gmail.com> wrote:

> I am going to buy a computer to run GAP. The main thing I am
> interested in are group presentations, Groebner bases and other
> memory-eating tasks. If anybody on the form has experience of running
> GAP on a computer with large RAM, can you answer whether 512 Gb is
> much better than 128 Gb. That is have you had problems that are solved
> by a computer with bigger RAM and not solved by a computer with
> smaller RAM?
> 
> Mark Sapir
> 
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