The daily edition.

1. Capability Overview

In core enterprise and mainframe architectures, online transactions (CICS/IMS) and batch jobs frequently update relational databases while simultaneously posting messages to queuing systems or modifying transactional files. Maintaining ACID integrity across these disparate data stores requires coordinated distributed transaction management.

Rocket Enterprise Server operates as an X/Open-compliant Transaction Manager (TM). It coordinates atomic Two-Phase Commit (2PC) processing across multiple heterogeneous Resource Managers (RMs)—including relational database management systems (IBM Db2, Oracle, Microsoft SQL Server, PostgreSQL) and messaging middleware (IBM MQ). Within Enterprise Server, each external participant configured to take part in two-phase syncpoint processing is managed as an XA Resource (XAR) (Planning and Designing XARs).

2. Architecture & How It Works

• The RM Switch Module (xa_switch_t): Enterprise Server interfaces with third-party database client libraries through an RM Switch Module—a shared library (.so on UNIX/Linux or .dll on Windows) (Building RM Switch Modules). The switch module exposes the standard X/Open xa_switch_t structure, supplying function pointers for core transaction operations:
  • xa_open() / xa_close() to manage connection lifecycles.
  • xa_start() / xa_end() to associate threads and transactions with branches.
  • xa_prepare(), xa_commit(), and xa_rollback() for two-phase commit execution.
  • xa_recover() to identify outstanding transactional units during failure recovery.
• Two-Phase Commit (2PC) Syncpoint Flow: When a COBOL program executes an EXEC CICS SYNCPOINT command or completes a transaction, Enterprise Server initiates Phase 1 (Prepare) across every enlisted RM. If all resource managers respond with XA_OK, Enterprise Server logs the commit decision and initiates Phase 2 (Commit). If any RM votes to abort or encounters an error during Phase 1, Enterprise Server automatically issues xa_rollback() across all participants, guaranteeing that partial updates are rolled back uniformly across both database and queue systems.
• In-Doubt Transaction Resolution via XA Logging: Unplanned outages—such as network disconnections, process termination, or database reboots between Phase 1 and Phase 2—leave transactions in an "in-doubt" state. Enterprise Server maintains a persistent XA Log to track active transaction branch identifiers (XIDs) (XA Recovery). Upon region startup or automatic reconnect, the TM invokes xa_recover() on the participating RMs, matches unresolved branches against the XA log, and issues the appropriate commit or rollback calls to restore database and messaging consistency.

3. Practical Configuration & Operational Tidbits

1. Defining XARs via ESCWA: To configure an XA resource, open ESCWA (Enterprise Server Common Web Administration), navigate to [Region] > General > XA Resources, and select New (To define an XA resource (XAR) for an enterprise server region). You must assign a unique XAR ID (used internally by JES batch jobs and CICS definitions), designate the full path to the compiled switch module (.so or .dll), and supply the database-specific Open string (XA Resource).
2. Formatting the Open String: The parameter string supplied in xa_open() is database-vendor specific. It generally bundles database names, DSN identifiers, user credentials, and threading models (such as DB=sample,UID=user,PWD=secret,TP=P for Db2 or connection strings for Oracle/PostgreSQL) (Generic one-phase commit for ODBC xa_open string).
3. Building Custom Switch Modules: Rocket provides standard COBOL source templates (e.g., ESMSSQL.CBL, ESODBCXA.CBL) in the product directories. Administrators compile these templates against their installed database client software using vendor-specific build scripts to ensure library alignment between 32-bit and 64-bit runtimes (Building RM Switch Modules).
4. Optimizing Single-Resource Workloads (1PC): If an application communicates with only a single database or an ODBC driver that does not natively implement two-phase commit, Rocket provides generic one-phase commit switch modules and bypass options to avoid the logging and messaging overhead of full 2PC coordination (Generic one-phase commit for ODBC xa_open string).

4. Reference Citations (Rocket Enterprise Server 12.0 Manuals)

• Planning and Designing XARs — Enterprise Server 12.0 for UNIX
• To define an XA resource (XAR) for an enterprise server region — Enterprise Server 12.0 for UNIX
• XA Resource — Enterprise Server 12.0 for UNIX
• XA Recovery — Enterprise Server 12.0 for UNIX
• Building RM Switch Modules — Enterprise Server 12.0 for UNIX
• RM Switch Module Registration — Enterprise Server 12.0 for UNIX
• Generic one-phase commit for ODBC xa_open string — Enterprise Server 12.0 for UNIX