Variable utils::mpiUidStride

Variable Documentation

constexpr unsigned long utils::mpiUidStride = 1UL << 40U

The width of the unique-ID range this process’s own rank owns.

When MPI is enabled, rank m’s UniqueIDManager (see that file) is seeded to start at m * mpiUidStride rather than 0, so that every rank’s own live-generated IDs are permanently non-overlapping, for the life of the run, with no need to ever rewrite an ID already written to disk. 2^40 (~1.1e12) is comfortably beyond the number of clusters any single rank could plausibly generate in one run, while still leaving room for up to 2^24 (~16.8 million) ranks before two ranks’ own ranges could ever meet, using the unsigned long (64-bit on every platform this code targets) IDs are stored as.