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A new connection specifier of the form FILEMAP = filemap-name associates a mapping with the opened file. If the file exists then the mapping must be one of the mappings allowed for the file. The set of allowed file mappings for an existing file is implementation dependent, but always includes the mapping under which the file was created. More generally, it will include any mapping where the file is mapped onto the same storage node arrangement, and with the same allocations of file records to storage nodes (different mappings may result in the same allocation of records to storage nodes). One choice is to allow any mapping, with possible degraded performance for ill matched mappings; another choice is to remap an existing file when it is opened with a new mapping, either offline or online. Vendors are expected to provide implementation dependent mechanisms to exercise such choices.
The default mapping is implementation dependent.
Only external files can be mapped.
Implementations may restrict the use of the FILEMAP connection specifier to files that are open for direct access (i.e., fixed size record files).