The arrival sequence access path for database files is based on
the order in which the records arrive and are stored in the file. This topic
discusses what kind of file can use arrival sequence access path and how you
can use the path to describe the file.
For reading or updating, records can be accessed:
- Sequentially, where each record is taken from the next sequential physical
position in the file.
- Directly by relative record number, where the record is identified by
its position from the start of the file.
An externally described file has an arrival sequence access path when no
key fields are specified for the file.
An arrival sequence access path is valid only for the following files:
- Physical files
- Logical files in which each member of the logical file is based on only
one physical file member
- Join logical files
- Views
You can use arrival sequence access paths in the following ways:
- Arrival sequence is the only processing method that allows a program to
use the storage space previously occupied by a deleted record by placing another
record in that storage space. This method requires explicit insertion of a
record given a relative record number that you provide. Another method, in
which the system manages the space created by deleting records, is the reuse
deleted records attribute that can be specified for physical files.
- Through your high-level
language, the Display Physical File Member (DSPPFM) command, and the Copy
File (CPYF) command, you can process a keyed sequence file in arrival sequence.
You can use this function for a physical file, a simple logical file based
on one physical file member, or a join logical file.
- Through your high-level language, you can process a keyed sequence file
directly by relative record number. You can use this function for a physical
file, a simple logical file based on one physical file member, or a join logical
file.
- An arrival sequence access path does not take up any additional storage
and is always saved or restored with the file. (Because the arrival sequence
access path is nothing more than the physical order of the data as it was
stored, when you save the data you save the arrival sequence access path.)