LOB data can be lengthy enough that it makes sense to load it from a LOBFILE. In LOBFILEs, LOB data instances are still considered to be in fields (predetermined size, delimited, length-value), but these fields are not organized into records (the concept of a record does not exist within LOBFILEs). Therefore, the processing overhead of dealing with records is avoided. This type of organization of data is ideal for LOB loading.
For example, you might have a table that stores employee names, IDs, and their resumes. When loading this table, you could read the employee names and IDs from the main data files and you could read the resumes, which can be quite lengthy, from LOBFILEs.
You might also use LOBFILEs to facilitate the loading of XML data. You can use XML columns to hold data that models structured and semistructured data. Such data can be quite lengthy.
Secondary data files (SDFs) are similar in concept to primary data files. Like primary data files, SDFs are a collection of records, and each record is made up of fields. The SDFs are specified on a per control-file-field basis. Only a collection_fld_spec can name an SDF as its data source.
SDFs are specified using the SDF parameter. The SDF parameter can be followed by either the file specification string, or a FILLER field that is mapped to a data field containing one or more file specification strings.