get considerations for GSAM and IMS™ message queues

For GSAM (generalized sequential access method) files in the IMS™ BMP or z/OS® batch environments, the following special considerations apply:

• get next is the only form of the get statement that you can use with GSAM.
• A single program cannot include a combination of add and get next statements for the same GSAM file.
• A get next statement for a serial record that is associated with a GSAM file results in a GN call to the GSAM database.
• If you read a variable-length serial record from a file that is associated with GSAM and the record length is longer than the physical file, DL/I returns a blank status code. Data is truncated, but no message is issued because the situation cannot be detected.

For serial files associated with an IMS™ message queue in the IMS™ BMP or z/OS® batch environments, the following special considerations apply:

• get next is the only form of the get statement that you can use with IMS™ message queues.
• A single program cannot include a combination of add and get next statements for the same IMS™ message queue.
• To use the get next statement for a serial file that is associated with an IMS™ message queue, you must associate the serial file with the I/O PCB.
• The get next statement is not supported for a textUI program or for a basic program that is called from a textUI program. Basic programs can associate only one serial input file with the I/O PCB. EGL automatically removes the IMS™ message header (length, ZZ field, and transaction code) from the message before moving the data to the serial record.
• A get next statement for a serial record that is associated with a single-segment message queue results in a GU call to the I/O PCB. This GU call results in an automatic commit point.
• The first get next statement for a serial record that is assigned to a multiple-segment message queue results in a GU call to the I/O PCB. Subsequent get next statements result in GN calls until a noRecordFound (status code QD) condition is reached. The first get next after the noRecordFound results in another GU call and this processing continues until an endOfFile (status code QC) is reached. Each GU call results in an automatic commit point.
• During any specific scheduling of a basic program, the program can use a get next statement for only one message queue. The transaction code for which IMS™ scheduled the program determines the message queue that is read. The system resource that is specified during generation is ignored.