In this case also, the rule applies that files should only be locked if it is vital for correct operation. Performance is reduced if too much emphasis is placed on safety considerations. It is possible that a lock or even SHARUPD mode can be avoided by allowing overbooking and by separating the component parts of records.
The use of the RELSE call to force a state of consistency for an open file should be used with caution because of the physical I/O operations involved.
Keyed accesses in ISAM are more complex than sequential accesses. If necessary they can be replaced in part by sequential accesses after the program or the file has been reorganized.
If files have to be accessed in a multiprocessor system, then the pros and cons of transferring a file or parts of it in advance should be considered. This depends on the structure of the file and of the accesses. It is also of great importance whether a multiprocessor system access can be executed via the network or via disks operated in shared pubset mode and which can be addressed by several processors.
If files are being created or extended, then an improvement in performance can be achieved by avoiding the secondary space allocation.
The more compact file structure which results from this gives rise to a variety of long-term improvements in performance.
It should also be mentioned at this point that parts of a file can be supported and monitored selectively by DAB (report “Reads resp.Writes for internal area” in the report group DAB of openSM2).