Casa6

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  Rui Xue <rx.astro@gmail.com> 3 days ago 826c31e116218750e0d4bd9668df49796f903cfe

  CAS-14756: Align image tile shape to MPI channel boundaries and disable explicit file locks
  The default casacore TiledShape could produce tiles that are
  small spatially but span many spectral channels. When mpicasa workers
  write to disjoint channel ranges of shared .residual/.psf/.sumwt images,
  their writes collide on the same physical disk tiles, causing Lustre
  table.lock contention that serializes all I/O (observed: ~22.5h on a
  29,861-channel dataset).
  
  SIImageStore::buildImage():
  - When chnchnks > 1 in itsMiscInfo, override PagedImage tile shape with
    TiledShape(min(Nx,256), min(Ny,256), Npol, Nchan/chnchnks), ensuring
    each MPI worker's channel range maps to independent tile blocks.
  - Serial mode (chnchnks absent or 1) falls back to the original
    PagedImage(shape, csys, name) constructor with casacore defaults.
  
  CubeMajorCycleAlgorithm:
  - subImageStore(): disable sumwt.lock(FileLocker::Write) — sumwt is only
    read for its shape, never written here.
  - getSubImage(): disable im->lock(FileLocker::Read) and im->unlock() —
    data is copied into a TempImage; no persistent write occurs.
  - writeBackToFullImage(): disable LatticeLocker and im->unlock() —
    workers write non-overlapping SubImage channel slices; tile alignment
    guarantees no shared disk blocks.
  
  Anticipate no metadata race risk: workers never call setImageInfo/setMiscInfo on
  disk images. All normalization operates on in-memory TempImage copies.
  Beam sets are serialized via MPI returnRec and merged by Rank 0 after
  all workers complete.

  • casatools/src/code/synthesis/ImagerObjects/CubeMajorCycleAlgorithm.cc (version 826c31e116218750e0d4bd9668df49796f903cfe) (diffs)
  • casatools/src/code/synthesis/ImagerObjects/SIImageStore.cc (version 826c31e116218750e0d4bd9668df49796f903cfe) (diffs)