Checkpoint-Restart Logic

Overview

Checkpointing is a pivotal concept in software development, particularly in scenarios involving transaction processing systems such as credit card transactions. Consider processing 50,000 transactions where a failure occurs after 40,000 — without checkpoint-restart, the entire batch must be restarted.

Solution Mechanism

Checkpoint-restart logic creates a checkpoint table or indexed file storing keys and relevant information. The system determines commit frequency based on processing speed and efficiency. Upon failure, the mechanism enables resumption from the point of failure rather than restarting from scratch.

Implementation Requirements

• The update program must distinguish between fresh runs and restarts
• Restart parameters are passed through JCL
• During restart, the program reads the checkpoint table, positions files to the last processed records, and resumes regular processing

Program Structure (CKPTPROG)

The implementation uses a COBOL-DB2-VSAM program with the following components:

• Input files: RL master file, random number files
• Work files: VSAM file for tracking, checkpoint file
• Output files: Load file, sold accounts file, error file

The FILE-CONTROL section defines sequential and indexed file organizations with appropriate file statuses for error handling.