The daily edition.

1. Capability Overview

IBM Information Management System (IMS) remains a cornerstone of high-volume transaction processing and hierarchical database management on z/OS mainframes. IMS workloads divide into two distinct functional domains: IMS Transaction Manager (IMS TM) and IMS Database (IMS DB / DL/I).

Rocket Enterprise Server provides native, production-grade emulation for both subsystems within its Mainframe Subsystem Support (MSS). This enables organizations to rehost complex IMS applications—including interactive Message Processing Programs (MPPs), background Batch Message Processing (BMP) programs, and batch DL/I jobs—onto distributed Linux/UNIX and Windows environments without restructuring hierarchical databases or recoding COBOL CBLTDLI and AERTDLI calls (Creating and Configuring an Enterprise Server Region for IMS).

2. Architecture & How It Works

• Transaction Processing Hierarchy (MPP, BMP, and ODBA): Rocket Enterprise Server accommodates all three core mainframe IMS execution patterns (IMS Database Locking):
  • Message Processing Programs (MPP): Online transactions triggered interactively by 3270 terminal users, asynchronous WebSphere MQ messages via the MQ-IMS Bridge (MQ-IMS Bridge), or distributed TCP/IP clients connecting through IMS Connect / OTMA (To enable IMS Connect).
  • Batch Message Processing (BMP): Long-running batch programs that access the shared IMS message queue to drain transaction queues while concurrently reading and updating online DL/I databases alongside active MPPs.
  • Open Database Access (ODBA): Allows JCL batch initiators, CICS regions, and external callers to execute direct DL/I calls against IMS databases using the AERTDLI call interface without requiring a full IMS message queue dispatch.
• Database Locking and IRLM: To maintain ACID consistency and prevent corrupting concurrent updates between online transactions and batch jobs, the IMS DB Control layer manages database segment locks. Enterprise Server provides two locking engines: Traditional Locking and the mainframe-equivalent Internal Resource Lock Manager (IRLM) (IMS Database Locking). IRLM maintains lock tables in shared memory and actively monitors for deadlock conditions, automatically resolving contention by rolling back the lower-priority transaction.
• TCP/IP Integration via IMS Connect & OTMA: Beyond standard TN3270 terminal emulation, modern web applications, microservices, and distributed middleware can drive IMS transactions directly over TCP/IP using IMS Connect emulation backed by Open Transaction Manager Access (OTMA) (To enable IMS Connect). The runtime automatically handles OTMA header parsing, character set conversion, and message routing into the IMS message queue.

3. Practical Configuration & Operational Tidbits

1. Leveraging the Pre-Configured IMSSIT: When establishing an IMS-enabled region, Rocket recommends basing the region's System Initialization Table on the supplied IMSSIT template (Configuring IMS Printers). IMSSIT pre-configures the initial transaction ID to /IMS (directing incoming 3270 terminal sessions immediately to the IMS TM screen) and associates the IMSSTRT startup list containing necessary resource groups like IMSGRP.
2. Configuring IMS Connect Listeners in ESCWA: To expose IMS TM to distributed TCP/IP clients, open ESCWA (Enterprise Server Common Web Administration), navigate to [Region] > General > Listeners > New Listener, specify protocol tcp, set conversion type to Custom, and define the conversion module as mfcs-ims-connect (To enable IMS Connect).
3. Dynamic Database Management Commands: Operators can control DL/I database availability dynamically using IMS system commands without cycling the server region (IMS DB system commands):
   • /STO DB <dbname> halts online access by MPPs and BMPs, enabling exclusive access for maintenance utilities or offline loads via IMSDBU.
   • /STA DB <dbname> re-opens and restores the database for online transaction processing.
4. Transaction Cataloging in ESMAC: IMS transactions can be created and reviewed in ESMAC by navigating to Resources > IMS > Transactions > New, where administrators configure transaction codes, associated COBOL application programs, and message class queue scheduling parameters (To define a transaction manually).

4. Reference Citations (Rocket Enterprise Server 12.0 Manuals)

• Creating and Configuring an Enterprise Server Region for IMS — Enterprise Server 12.0 for UNIX
• To enable IMS Connect — Enterprise Server 12.0 for UNIX
• IMS Database Locking — Enterprise Server 12.0 for UNIX
• IMS DB system commands — Enterprise Server 12.0 for UNIX
• Configuring IMS Printers — Enterprise Server 12.0 for UNIX
• MQ-IMS Bridge — Enterprise Server 12.0 for UNIX
• To define a transaction manually — Enterprise Server 12.0 for UNIX