add considerations for GSAM and IMS message queues

Special considerations apply to the following cases in the IMS BMP or z/OS® batch environments:
  • serial files implemented as GSAM (generalized sequential access method) files
  • IMS message queues
In either of these cases, be aware of the following considerations:
  • An add statement for a serial record that is associated with a sequential (non-VSAM) file adds data to the beginning of the file and loses all previous data, unless the file is allocated using DISP=MOD in the JCL for the batch job. Until the file is closed, subsequent add statements place data following the previously added data.
  • A single program cannot include a combination of add and get next statements for the same GSAM file.
  • An add statement for a serial record associated with a GSAM file results in an ISRT call to the GSAM database. The program starts adding the records at the beginning of the file unless the file is allocated using DISP=MOD in the JCL for the batch job. Until the file is closed, subsequent add statements place data following the previously added data.
  • If you add a variable-length serial record to a file 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.