There are several things of which you should be aware when using multiple-record mode:
In other words, when the server sends a collection of records to a client, that client now has a snapshot of the records on the server. The client does not query the server about any new records, since this would remove the performance gain of using multiple-record mode.
As the user executes READ NEXT, that record never appears. For example, suppose the file has a key that is a PIC 99 data item, and that ten records are sent in each batch. Also suppose that the file has records with keys 05, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95. The user opens the file and executes a READ NEXT. At this time, the first ten records are in the client cache (records 05, 10, 15, 20, 25, 30, 35, 40, 45, 50) and the COBOL program has record 05 in its record area. Suppose the user then executes a WRITE to write a record with the key of 08 and then executes another READ NEXT. The record that the COBOL program has in its record area is now record 10, not record 08. Again, the client and server will not communicate about this situation, since it would completely remove the performance gain of using multiple-record mode.
Since multiple-record mode is inherently subject to race conditions, you should use this mode only in situations in which you are sure you understand all of the consequences.