This mode only applies to ISAM-A files implemented under D-ISAM. When activated, it forces any write operation to wait until the data has actually been committed to disk before returning to the program. This will dramatically slow down access but might be useful in certain networked situations where you want to eliminate the possibility of a user on another CPU reading an outdated copy of the data due to buffer synchronization problems. It may also be useful in extremely critical applications where you cannot afford the possibility that a system crash will leave a lot of uncommitted updates stranded in memory.