If you’re updating the PF, this should have very little impact on performance – logical files are in effect only indexes over the data in physical files and don’t contain copies of the data. The index will only need to be updated if there’s an impact on the key in the logical file. This will need to be done whether you select all the fields in the PF or one field in the PF.

Regarding updates/inserts on such a logical – if you insert a record through a logical with only selected fields, the fields not selected in the LF will be filled with default values in the PF – this can cause problems for applications as some of these fields may have defaults of NULL values which many applications can’t handle. With an update, only the fields selected in the LF are available for update within your application.

Regards,

Martin Gilbert.