[Paraview] Programmable filter in parallel

[Tim Gallagher]

I guess I sort of answered my own question -- the entire script runs on each processor, so I ended up with 8 copies of my data in memory (or I would have, had I not filled the 12 GB of RAM and 20 GB of swap space and my system crashed). 

So is there some way to query the processor information? Probably something in the RequestInformation script -- find out how many processors there are and then the prog. filter determines based on processor ID and number of processors what section of the data to load. 

In that case, how does the aggregation of the data work? The exact pipeline is:

DataObjectGenerator("MB{}")
ProgrammableFilter

in serial, the PF appends blocks into the input and passes that through to the output. In parallel, that same pipeline would create a MB{} on each CPU that gets filled with that CPU's data, but at the end of this step I would want a single MB{} object, not NCPU MB{}'s. 

Hopefully that makes sense... I've never used PV in parallel, so I'm not sure how it all works.

Tim

----- Original Message -----
From: "Tim Gallagher" <tim.gallagher at gatech.edu>
To: "ParaView list" <paraview at paraview.org>
Sent: Wednesday, August 3, 2011 9:24:25 AM
Subject: [Paraview] Programmable filter in parallel

Hi,

I know many of the built-in readers/filters already work in parallel, but how does one write a parallel programmable filter?

Our data files are XDMF and split into blocks of data. We have a single XDMF file that we can read that reads all the blocks and generates a vtkMultiBlockDataset (this works with the built in XDMF reader). 

However, each block has some ghost cells around it that are needed to do the CellDataToPointData interpolation. For large numbers of blocks, this creates far too many grid points for our machines to load. So, I've written a programmable filter that does:

start with empty vtkMultiBlockDataset
for each block in restart file
   read block file with XDMFReader
   CellDataToPointData
   strip off the extra layers of cells
   append to output vtkMultiBlockDataset

If I run this in parallel, what exactly is parallel? Is the reading and CD2PD done in parallel on each block? Is none of it parallel? Ideally, I would have the loop over blocks done in parallel, but I don't know how to indicate that in the programmable filter (if it's possible).

Any advice would be great,

Tim
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