1.5 What about Performance?
One of the goals of netCDF is to support efficient access to small
subsets of large datasets. To support this goal, netCDF uses direct
access rather than sequential access. This can be much more efficient
when the order in which data is read is different from the order in
which it was written, or when it must be read in different orders for
different applications.
The amount of overhead for a portable external representation depends
on many factors, including the data type, the type of computer, the
granularity of data access, and how well the implementation has been
tuned to the computer on which it is run. This overhead is typically
small in comparison to the overall resources used by an
application. In any case, the overhead of the external representation
layer is usually a reasonable price to pay for portable data access.
Although efficiency of data access has been an important concern in
designing and implementing netCDF, it is still possible to use the
netCDF interface to access data in inefficient ways: for example, by
requesting a slice of data that requires a single value from each
record. Advice on how to use the interface efficiently is provided in
Structure.
The use of HDF5 as a data format adds significant overhead in metadata
operations, less so in data access operations. We continue to study
the challenge of implementing netCDF-4/HDF5 format without
compromising performance.
