I've been trying to tackle tt #1742, #1890, and #1893 as part of some I/O work that uses large datatypes. Am I stepping on anyone's toes here? Pavan, I know i bugged you about these tickets. Hope I didn't waste my Thursday on this... Pavan told me there are two problems here, but I think there are really one solution to both: - large datatype means a datatype that describes more than 2 gigs of data. A million contigs of a million contigs, say - large count means datatypes that use MPI_Count to say how many elements they have: a contig of 3 billion MPI_BYTES, say Internally, though, there's no way to decouple those two problems. The changes are pervasive and make me really nervous. I've been sometimes pushing changes to the ticket-1742-bigio branch. Who can review datatype changes once I'm done?: ==rob -- Rob Latham Mathematics and Computer Science Division Argonne National Lab, IL USA