Rationale

The internal COBOL sort function is known as being inefficient on zOS environment (this is the same problem with the merge function). It is often recommended to use external sort tools to process files which can contain a large number of records. Usually required in batch processing the sort tools are generally called by a previous step in the JCL running the program.
Using the internal Cobol sort function rather than external sort tool can affect perceptibly the performance of applications in terms of data manipulation.