The Internal Interface may be used to allocate records for a variable
in a single-file CDF.
Normally the number of records allocated would be the number that are
to be written (assuming this can be determined).
This can greatly improve performance when writing (and reading) values
for the variable because of reduced overhead when searching the index
entries (as described in Section 2.2.7). The application
is expected to write to all of the allocated records. When the CDF is
closed, any allocated records for a variable
which have not yet been written are
written using the pad value for the variable.
Records may only be allocated for a variable once but any number of
records can eventually be written to the variable. For NRV variables,
only one record may be allocated (because only one record will ever
physically exist).
Performance is improved when using this method because the allocated records will be contiguous and will require only one index entry. This will greatly improve the time needed to locate a particular record when the variable is accessed. In addition, the CDF will be slightly smaller because of the reduced number of index records needed per variable.
Records are allocated using the <PUT_,rVAR_ALLOCATERECS_> and <PUT_,zVAR_ALLOCATERECS_>> operations of the Internal Interface.