IMS DB IO Area
The IO-area is the data area for the segment.
The Io-area is the storage location for the segment to be processed which passes to IMS.
Io-areas are a two way communication.
For read calls, IMS places the segment retrieved in the Io-area.
For update calls, the program must place updated segment in the Io-area and IMS will update the database with updated io-area.
The length of the Io-area is also very important and may or may not be same as the length specified in DBD.
IMS takes the segment length from the DBD and will not consider the Io-area length.
If the IO-area in the program
If the Io-area in the program is too short, IMS will overlay the subsequent storage after Io-area.
If the Io-area is too long; IMS will ignore the extra positions.
To update or delete a segment in IMS, the application program must first read and lock the particular segment which requires updating or deleting.
Otherwise, application program can’t able to update or delete any segment.IMSDB PCB Mask IMSDB SSA