Data offset
The data offset indicates the data that should not be compressed or expanded when the compression or expansion starts at a point other than the beginning of the record. The offset for fixed and variable-length records is illustrated in the following examples.
For fixed-length records, the offset is equal to the bytes of data that should not be compressed. For example, if you do not want to compress the first 4 bytes of each record, use a data offset of 4. Compression will begin with the fifth byte, as shown in the following example. When you expand a compressed record, use the same offset value. Data Packer detects that the compressed record starts with a logical length (LL) value and processes the record with the value included.
For variable-length or unformatted records, the offset is equal to the bytes of data that should not be compressed plus 2 bytes. For example, if you do not want to compress the first 4 bytes of each record, use a data offset of 6. Compression will begin with the seventh byte. This action occurs because each variable-length record begins with the 2-byte logical length (LL) of the record.
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