If your program processes a database file sequentially for input
only or output only, you might be able to improve performance using the sequential-only
processing (SEQONLY) parameter on the Override with Database File (OVRDBF)
or the Open Database File (OPNDBF) command.
To use SEQONLY processing, the file must be opened for input-only or output-only.
The NBRRCDS parameter can be used with any combination of open options. (The
Open Query File (OPNQRYF) command uses sequential-only processing whenever
possible.) Depending on your high-level language specifications, the high-level
language can also use sequential-only processing as the default. For example,
if you open a file for input only and the only file operations specified in
the high-level language program are sequential read operations, then the high-level
language automatically requests sequential-only processing.
Note: File positioning
operations are not considered sequential read operations; therefore, a high-level
language program containing positioning operations will not automatically
request sequential-only processing. (The SETLL operation in the RPG/400® language
and the START operation in the COBOL/400® language are examples of
file positioning operations.) Even though the high-level language program
cannot automatically request sequential-only processing, you can request it
using the SEQONLY parameter on the Override with Database File (OVRDBF) command.
If you specify sequential-only processing, you can also specify the number
of records to be moved as one unit between the system database main storage
area and the job's internal data main storage area. If you do not specify
the sequential-only number of records to be moved, the system calculates a
number based on the number of records that fit into a 4096-byte buffer.
The system also provides you a way to control the number of records that
are moved as a unit between auxiliary storage and main storage. If you are
reading the data in the file in the same order as the data is physically stored,
you can improve the performance of your job using the NBRRCDS parameter on
the OVRDBF command.
Note: Sequential-only processing should not be used with
a keyed sequence access path file unless the physical data is in the same
order as the access path. SEQONLY(*YES) processing might cause poor application
performance until the physical data is reorganized into the access path's
order.