By suppressing the evaluation of all ISAM keys, ISAM record retrieval performance can be enhanced. For each user, each ISAM data file is assigned a set of key buffers containing the current key image of each index for the current ISAM position. To speed record access, UpdateHeader() accepts a mode, ctISAMKBUFhdr, which toggles support of the key buffers for a particular ISAM data file for the calling user.
Key buffer support is enabled/disabled with UpdateHeader() as shown in the sections below:
Several considerations apply.