In addition to change verify, record locking is supported in DP4 as a control that you can apply in your application program. You can specify record locking in your program to ensure that the first user to read a record has the exclusive right to update the record. Other users are not allowed to update the record until the first user has completed the update.
Record locking differs from change verify since the locking is done to the record when it is read by the first user. If the user is slow in completing the transaction, the record may be locked for some time, which can cause problems to other users, or even cause dead-lock (where two users each want to lock a record that the other has already locked and will not unlock the record they already ahve locked). The change verify procedure gives priority to the first of the users to attempt an update. Of the two methods, change verify gives the better performance when the incidence of contention is low.
You are recommended to use record locking sparingly.