[petsc-dev] GAMG key not found in table

[Smith, Barry F.]

  Pierre,

    Can you confirm if my suggested fix resolved the error message or not? If so, we'll add it to the maint branch.

   Thanks

    Barry


https://stackoverflow.com/questions/11720656/modulo-operation-with-negative-numbers



> On Jun 24, 2018, at 4:19 PM, Mark Adams <mfadams at lbl.gov> wrote:
> 
> 
> 
> On Sun, Jun 24, 2018 at 2:09 PM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:
> 
> 
> > On Jun 24, 2018, at 11:15 AM, Mark Adams <mfadams at lbl.gov> wrote:
> > 
> > First, -pc_gamg_threshold 0.8  is crazy. 0.08 is very high. probably best to start with 0.
> > 
> > This threshold will delete all of your edges in the coarsening graph, probably, and GAMG will switch to a one level solve (silently although -info will tell you).
> > 
> > And yes, this looks like a 64 bit indices problem, we have:
> > 
> > #define GAMG_HASH(key) ((((PetscInt)7)*key)%a_tab->size)
> > 
> > We should probably cast everything to (long long) or (unsigned PetscInt) I guess ... I'm not sure how this should be done exactly.  Any ideas from the peanut gallery?
> 
> Mark,
> 
>      It should only be changed if we know the exact mechanism that causes the failure. It is not obvious to me that just changing ((((PetscInt)7)*key)%a_tab->size) to ((((PetscInt64)7)*key)%a_tab->size) should matter.
> 
> If 7*key > 2B then you can get a negative number and %a_tab->size will still be a negative number, which triggers:
> 
> ksp/pc/impls/gamg/agg.c:          if (flid < 0) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Cannot find gid1 in table”);
>  
> which is the second error that Pierre gets. I don't fully understand the first error but a messed up hash table is certainly a possibility.
> 
> And maybe we should cast the hell out of it to be safe:
> 
> #define GAMG_HASH(key) (PetscInt)((((PetscInt64)7)*(PetscInt64)key)%(PetscInt64)a_tab->size)
> 
> I am a bit puzzled that this works. I would think this would be more of a problem but maybe everyone just uses 64 bit ints. I have dealt with this many times and I am puzzled that I left it in a state that looks so wrong to me now. Perhaps Pierre's complicated thing is causing this somehow.
> 
> 
> 
>    Barry
> 
> > 
> > 
> > 
> > On Sun, Jun 24, 2018 at 2:34 AM Pierre Jolivet <pierre.jolivet at enseeiht.fr> wrote:
> > Hello,
> > Any ideas on how to debug this?
> > [406]PETSC ERROR: key 328214936 not found in table
> > [406]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble shooting.
> > [406]PETSC ERROR: Petsc Development GIT revision: v3.9.2-603-gceafe64  GIT Date: 2018-06-10 12:46:16 -0500
> > [406]PETSC ERROR: /ccc/work/cont003/rndm/rndm/FreeFem-sources/src/mpi/FreeFem++-mpi on a arch-linux2-c-debug-bullxmpi named curie2698 by jolivetp Sun Jun 24 07:06:07 2018
> > [406]PETSC ERROR: Configure options --with-scalar-type=real --with-hypre-dir=arch-linux2-c-opt-bullxmpi --with-metis-dir=arch-linux2-c-opt-bullxmpi --with-mumps-dir=arch-linux2-c-opt-bullxmpi --with-mkl_cpardiso=1 --with-mkl_pardiso=1 --with-parmetis-dir=arch-linux2-c-opt-bullxmpi --with-ptscotch-dir=arch-linux2-c-opt-bullxmpi --with-sowing-dir=arch-linux2-c-opt-bullxmpi --with-blacs-include=/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl/include --with-blacs-lib=/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl/lib/intel64/libmkl_blacs_openmpi_lp64.so --with-blaslapack-dir=/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl/lib/intel64 --with-x=0 --with-debugging=1 --with-errorchecking=1 --with-mkl_pardiso-dir=/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl --with-mkl_cpardiso-dir=/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl --with-scalapack-include=/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl/include --with-scalapack-lib="[/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl/lib/intel64/libmkl_scalapack_lp64.so,/ccc/products/mkl-18.0.1.163/default/18.0.1.163/mkl/lib/intel64/libmkl_blacs_openmpi_lp64.so]" --with-fortran-bindings=0 PETSC_ARCH=arch-linux2-c-debug-bullxmpi
> > [406]PETSC ERROR: #1 PCGAMGHashTableFind() line 106 in /ccc/work/cont003/rndm/rndm/petsc/include/petsc/private/pcgamgimpl.h
> > [406]PETSC ERROR: #2 smoothAggs() line 526 in /ccc/work/cont003/rndm/rndm/petsc/src/ksp/pc/impls/gamg/agg.c
> > [406]PETSC ERROR: #3 PCGAMGCoarsen_AGG() line 970 in /ccc/work/cont003/rndm/rndm/petsc/src/ksp/pc/impls/gamg/agg.c
> > [406]PETSC ERROR: #4 PCSetUp_GAMG() line 518 in /ccc/work/cont003/rndm/rndm/petsc/src/ksp/pc/impls/gamg/gamg.c
> > [406]PETSC ERROR: #5 PCSetUp() line 932 in /ccc/work/cont003/rndm/rndm/petsc/src/ksp/pc/interface/precon.c
> > [406]PETSC ERROR: #6 KSPSetUp() line 381 in /ccc/work/cont003/rndm/rndm/petsc/src/ksp/ksp/interface/itfunc.c
> > 
> > For smaller problems, this works fine. Should I compile using 64 bit indices?
> > I’m using -pc_type gamg -pc_gamg_threshold 0.8 -pc_gamg_agg_nsmooths 1 -pc_gamg_sym_graph true -pc_gamg_square_graph 10
> > 
> > Thanks,
> > Pierre