Enable collective MPI IO. #623
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* Enable collective I/O when reading/writing slices * Make test datatypes match in memory and in file While it's perfectly legal for memory and file to differ, HDF5 will "break collectives" and do the transfer independently. See H5Pget_mpio_no_collective_cause() documentation for other reasons collectives might break. * debugging: report why collective I/O didn't happen
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@roblatham00 would this variation work for your applications? |
| << std::endl; | ||
| throw std::runtime_error("IO wasn't collective."); | ||
| } else { | ||
| std::cout << "Success! The operation was collective.\n"; |
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Thanks for adding an example of how to obtain the property list and query it. In a parallel test, this output will clutter the screen so can we delete the "Success" and emit text only if an error?
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I know this is an example, and clients can do whatever they want with highfive, but I think throwing a runtime error is overkill for this condition. The user requested collective i/o, HDF5 library was unable to perform I/o collectively (for whatever reason), but did perform I/O independently.
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Good point. The intention behind throwing is that we run the examples a part of our CI. So what you've spotted is that I'm abusing the examples as a test that the request for collective I/O was forwarded correctly to HDF5.
It doesn't cover collective reads, nor all of the entry points. I'll add proper test coverage for this; which frees up the example to be purely instructional. Thank you!
We now clearly state what it means that the operation failed to use MPI collectives. Additionally, noisy output has been removed.
Add unit-tests for writing/reading collectively & independently.
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By merging, I'd like to free up other PRs which are blocked by this one. If there's any changes anyone would like to propose, please do so. |
This PR adds the ability to pass a data transfer property list to
readandwriteoperations. This is needed to enable collective MPI-IO.In essence this is #621