[MOAB-dev] Re: parallel read bug, interface awkwardness

[Jed Brown]

On Mon 2008-09-22 10:25, Jed Brown wrote:
> I have identified a MOAB parallel read bug.  It appears that if all
> nodes of an edge or face are shared, MOAB sometimes assumes that the
> edge/face is also shared.  This is incorrect since the face might
> actually be a boundary face.  I think that if
> 
> 0 --- 1 --- 2
> |  A  |  B  |
> 3 --- 4 --- 5
> |  C  |  D  |
> 6 --- 7 --- 8
> |  E  |  F  |
> 9 --- 10 -- 11
> 
> appears on a boundary where proc 0 owns all faces except face D which is
> owned by proc 1.  Then proc 0 will own all edges except 5-8, but proc 1
> will think that 5-8 and face D are also owned by proc 0.  The attached
> tarball demonstrates the issue.  If you unpack and run `make break' you
> will see that the shared sets don't agree.  Run `make repartition' to
> produce a new partition (likely different because mbzoltan is
> nondeterministic).  I have run `make repartition break' a few times and
> there are always sets which don't agree.

To follow up on this, a recent patch has greatly improved the quality of
mbzoltan partitions.  At least for simple cases, these partitions do not
have the property mentioned before.  However, the read bug still exists
for these `pathological' partitions such as the one attached in my
previous message.  To reproduce, just unpack and run `make break'.
Hopefully someone more familiar with the parallel read knows how to fix
this.

A sufficiently complex mesh may not be partitionable in a way which
avoids this so it's really not okay to assume that the process which
owns the vertices also owns the entity; it may not be adjacent to any
owned region.  This matters to me because edges and faces are used
explicitly as part of my function space.

Jed
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