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Incorporate Dave Allured's documentation

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Dennis Heimbigner 2022-02-28 14:40:35 -07:00
parent a698b919c1
commit bbbc72739f
1 changed files with 33 additions and 4 deletions
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libsrc4/nc4internal.c
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@ -2006,13 +2006,42 @@ NC_freeglobalstate(void)
/* Specific property functions */
/**
Provide set function to store global data alignment
information and apply it when a file is created.
Provide a function to store global data alignment
information.
Repeated calls to nc_set_alignment will overwrite any existing values.
If defined, then for every file created or opened after the call to
nc_set_alignment, for every new variable added to the file, the
nc_set_alignment, and for every new variable added to the file, the
most recently set threshold and alignment values will be applied
to that variable.
Repeated calls to nc_set_alignment will overwrite any existing values.
The nc_set_alignment function causes new data written to a
netCDF-4 file to be aligned on disk to a specified block
size. To be effective, alignment should be the system disk block
size, or a multiple of it. This setting is effective with MPI
I/O and other parallel systems.
This is a trade-off of write speed versus file size. Alignment
leaves holes between file objects. The default of no alignment
writes file objects contiguously, without holes. Alignment has
no impact on file readability.
Alignment settings apply only indirectly, through the file open
functions. Call nc_set_alignment first, then nc_create or
nc_open for one or more files. Current alignment settings are
locked in when each file is opened, then forgotten when the same
file is closed. For illustration, it is possible to write
different files at the same time with different alignments, by
interleaving nc_set_alignment and nc_open calls.
Alignment applies to all newly written low-level file objects at
or above the threshold size, including chunks of variables,
attributes, and internal infrastructure. Alignment is not locked
in to a data variable. It can change between data chunks of the
same variable, based on a file's history.
Refer to H5Pset_alignment in HDF5 documentation for more
specific details, interactions, and additional rules.
@param threshold The minimum size to which alignment is applied.
@param alignment The alignment value.