[petsc-users] On the edge of 2^31 unknowns

[Eric Chamberland]

Barry,

I can't launch the code again and retrieve other informations, since I 
am not allowed to do so: the cluster have around ~780 nodes and I got a 
very special permission to reserve 530 of them...

So the best I can do is to give you the backtrace PETSc gave me... :/
(see the first post with the backtrace: 
http://lists.mcs.anl.gov/pipermail/petsc-users/2015-November/027644.html)

And until today, all smaller meshes with the same solver succeeded to 
complete... (I went up to 219 millions of unknowns on 64 nodes).

I understand then that there could be some use of PetscInt64 in the 
actual code that would help fix problems like the one I got.  I found it 
is a big challenge to track down all occurrence of this kind of overflow 
in the code, due to the size of the systems you have to have to 
reproduce this problem....

Eric


On 16/11/15 12:40 PM, Barry Smith wrote:
>
>    Eric,
>
>      The behavior you get with bizarre integers and a crash is not the behavior we want. We would like to detect these overflows appropriately.   If you can track through the error and determine the location where the overflow occurs then we would gladly put in additional checks and use of PetscInt64 to handle these things better. So let us know the exact cause and we'll improve the code.
>
>    Barry
>
>
>
>> On Nov 16, 2015, at 11:11 AM, Eric Chamberland <Eric.Chamberland at giref.ulaval.ca> wrote:
>>
>> On 16/11/15 10:42 AM, Matthew Knepley wrote:
>>> Sometimes when we do not have exact counts, we need to overestimate
>>> sizes. This is especially true
>>> in sparse MatMat.
>>
>> Ok... so, to be sure, I am correct if I say that recompiling petsc with
>> "--with-64-bit-indices" is the only solution to my problem?
>>
>> I mean, no other fixes exist for this overestimation in a more recent release of petsc, like putting the result in a "long int" instead?
>>
>> Thanks,
>>
>> Eric
>>