Overview of the IBM MVS System Logger
Article ID: 37285
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Summary:
The IBM MVS System Logger is a component which provides a set of services for the writing, reading, and management of log streams. The majority of MVS System Logger functions execute in a separate address space named IXGLOGR on each member of the SYSPLEX.
A log stream is a chronologically ordered set of application specific data that is generally used for maintaining event histories, such as transaction and recovery logs. The MVS System Logger does not impose any particular structure or format of the data comprising an application log stream.
Examples of MVS system components that can be configured to use the MVS System Logger are LOGREC Recording and the MVS Operations Log (OPERLOG).
Instructions:
The major strengths and characteristics of the MVS System Logger services are:
- Robustness.
The underlying facilities provide a very high degree of data integrity and availability. The data storage mechanisms allow for the duplexing and recovery of vital data. These actions are performed without the need for direct involvement by the application. However, the application is made aware of data unavailability (permanent or temporary) and the application can participate in recovery management processing. - Data sharing coordination and integrity.
The MVS System Logger, not the application, coordinates all log stream activities, both within a given system and across multiple systems in the SYSPLEX. This coordination ensures the consistency and integrity of the data contained within the log stream. - Data management over time.
Through log stream policy definitions, the MVS System Logger manages the residency and movement of log stream data over time. Facilities exist for the offloading of log stream data to secondary storage. This activity takes place automatically as log stream data ages as well as when the primary log stream data storage areas reach storage consumption thresholds. Additionally, the application may itself initiate these activities.
In general, applications reading log streams are not aware of and need not be concerned with the location of log stream data. - Device independence.
From the application perspective, log streams are purely logical data streams. Applications have no knowledge of the physical devices on which the log streams reside.
The MVS System Logger supports two types of log streams:
- Coupling Facility A Coupling Facility based log stream uses a coupling facility list structure for its primary level of interim storage. This type of log stream can be shared by multiple instances of an application across multiple systems in the SYSPLEX.
- DASD only
A DASD-only log stream uses VSAM Linear data sets for its primary level of interim storage. This type of log stream can be shared by multiple instances of an application on a single system only. It cannot be shared across multiple systems in the SYSPLEX.
An installation can use both types of log streams for various applications concurrently.
All log stream definitions and associated characteristics are contained in the LOGR Couple Data Set. This collection of information is generally referred to as Log Stream Policy Information. The LOGR couple data set must be accessible by all the systems in the SYSPLEX and is initially constructed and formatted by the IXCL1DSU utility. Policy information is maintained by executing the IXCMIAPU utility as well as through the IXGINVNT service.
CA SYSVIEW provides several commands which operate upon data contained in system log streams.
The OPERLOG command displays the contents of the MVS Operations Log. The data contained within this log stream is a superset of what is contained in the traditional MVS SYSLOG. An installation can choose to use either or both of these message logging facilities. If the OPERLOG is to be used, it must be named SYSPLEX.OPERLOG and can be either Coupling Facility or DASD Only based. When using a coupling facility based OPERLOG, the information from the participating members of the SYSPLEX is logically merged by the MVS System Logger into a single chronologically ordered log stream.
The LOGREC command displays the contents of the MVS error recording log. The traditional location of this information is the SYS1.LOGREC data set. Much like the Operations Log, the installation can choose to collect the error recording log data in an MVS System Logger log stream instead of the SYS1.LOGREC data set. This log stream can be either coupling facility or DASD only based.
The following IBM publications contain detailed information about the MVS System Logger as well as the processes the installation must follow to exploit the MVS System Logger for the Operations Log and Error Recording facilities:
GA32-0905 z/OS Diagnosis: Tools and Service Aids
SA23-1390 z/OS MVS Planning: Operations
SA23-1368 z/OS MVS Programming: Assembler ServicesGuide
SA23-1371 z/OS MVS Programming: Authorized AssemblerServices Guide
SA23-1399 z/OS MVS Setting Up a Sysplex
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