The data file part of an indexed file contains all the data records.
Information about free records in the data file is maintained so that space created by deleting records can be re-used, preventing the file from growing too quickly.
In a fixed-format indexed file, this information is held in a free space record in the index file. This record has the same structure as the index free space record, but the addresses point to data file records.
In a variable-format indexed file, the information is held in a system record in the data file. All records are a multiple of the data record alignment size. For each slot length, a chain is maintained for all slots of that length that are free. The start of the chain for all lengths is maintained in the data free space record in the data file. This system record is always the same length as the maximum slot length or possible maximum compressed length (a record's length may increase when it is compressed) for the file. Each free slot pointed to contains, in the first n bytes after the record header, the address of the next free slot of the same length. For the last slot in the chain, this address contains zero.
The data free space record contains:
|Offset||Size||Description of the field|
|2/4||4||Offset of the first free data slot of length 8 bytes.|
|6/8||4||Offset of the first free data slot of length 12 bytes.|
|n||4||Offset of the first free data slot of maximum length.|