Architecture: JES and Batch Processing

Every night, while the bank's tellers have gone home and the CICS transaction load has dropped to near zero, a different kind of work begins. Millions of account records are updated with interest. Every transaction from the trading day is reconciled. Customer statements are generated. Risk models are recalculated. None of this work has a user waiting for a response. None of it runs in real time. It runs in batch. Batch processing is the other… Read More

Architecture: DB2 for z/OS

A payment transaction hits the mainframe. It needs to check an account balance, verify a credit limit, write an audit record, and update three tables atomically. All of this happens under a single unit of work, coordinated by a database that has been running at that bank since the 1980s. If any part fails, every change rolls back. If two transactions try to update the same row simultaneously, one waits. If the system crashes mid-transaction, the… Read More

Architecture: VSAM

Every time a CICS transaction reads an account record, there is a file somewhere holding that record. It is not a relational table. It is not a flat file. It is a VSAM dataset: a structured, indexed file that CICS reads in under 10 milliseconds, keyed precisely on the account number, without scanning from the beginning. VSAM is the file system that mainframe application programs live on. Every CICS file definition points to a VSAM dataset. Every … Read More