ESS Concepts and Components
ESS provides real-time delivery of IBM® Connect:Direct® event records to interested application interfaces. ESS is based on the existing IBM Connect:Direct statistics facility and is designed to:
- Minimize the server-performance overhead for ESS processing
- Prevent adverse impact on IBM Connect:Direct server reliability
ESS is a low-level IBM Connect:Direct server technology that enables you to layer multiple APIs. An end-user application interfaces with the API rather than the low-level ESS core technology. This design enables future extension of ESS to support multiple application interface protocols and publishing of the same event data to several event consumer applications.
ESS supports the event services exit and the CICS API interface.
An application can access event data through an ESS exit. A sample event exit (DGAXEV01) is in the sample library, and writes the event data to a predefined data set.
A CICS API initiates event processing by signing on to IBM Connect:Direct through the current CICS API and issuing ESS commands. The CICS API provided with IBM Connect:Direct writes event data to a CICS Transient Data Queue (TDQ). A sample program, DGAQ249, shows how to read an event record from the TDQ.
- Event Definition
Because ESS event records are IBM Connect:Direct statistics records, ESS does not restrict events to abnormal activities. This design enables ESS-enabled applications to initiate procedures based on either successful or unsuccessful Process statements.
- Historical Data Recovery
The IBM Connect:Direct statistics file functions as the historical repository of ESS event data. ESS supports optional automated recovery of past event data if an event consumer application fails. Upon restart, ESS requests old event records from the statistics file.
The API automatically manages the restart point for an ESS-enabled application. This API tracks the last successfully delivered event record to a designated subscriber. Upon restart, the API resynchronizes event processing by issuing a SELect STATistics command to retrieve the historical event data and deliver it to the restarted event consumer.
- Event Record Types
The event record types give external applications greater visibility into IBM Connect:Direct activities and improve the reliability and responsiveness of interface applications in a production environment. ESS supports several IBM Connect:Direct event record types, including:
- Process Initialization (PI) occurs immediately prior to the execution of the first Process statement in a Process.
- Step Start (CI, JI, TI) events occur immediately prior to the execution of a COPY, RUN JOB, or RUN TASK statement.
- COPY Step I/O Start (CE) occurs just before the first COPY step I/O in a Process.
- Queue Change (QW, QH, QE, QT) events occur whenever a Process moves from one logical queue to another in the TCQ. The sample initialization parameters provided in the base IBM Connect:Direct install the $CD.SDGAPARM data set and specify STAT.EXCLUDE=(QE, QH, QT, QW). This specification prevents IBM Connect:Direct from producing the queue change records. If you want queue change records, you must set this parameter appropriately.
- A fault management application can request notification of COPY requests that did not complete normally, QH (Queue Hold) events or both. When such an event occurs, the fault management application can then poll IBM Connect:Direct through SELect STATistics or SELect PROCess to investigate the problem further.
- An application registers interest in all events for a small group of mission-critical Processes.