What is system logger?
System logger is an MVS™ component
that allows an application to log data from a sysplex. You can log
data from one system or from multiple systems across the sysplex.
A system logger application can be supplied by:
- IBM®. For example, CICS® log manager and the operations log stream (OPERLOG) are IBM-supplied system logger applications.
- Independent software vendors.
- Your installation.
A system logger application can write log data into a log
stream, which is simply a collection of data. Data in a log stream
spans two kinds of storage:
- Interim storage, where data can be accessed quickly without incurring DASD I/O.
- DASD log data set storage, where data is hardened for longer term access. When the interim storage medium for a log stream reaches a user-defined threshold, the log data is off-loaded to DASD log data sets.
There are two types of log streams: coupling facility log streams
and DASD-only log streams. The main difference between the two types
of log streams is the storage medium system logger uses to hold interim
log data:
- In a coupling facility log stream, interim storage for log data is in coupling facility list structures. See Coupling facility log stream.
- In a DASD-only log stream, interim storage for log data is contained in local storage buffers on the system. Local storage buffers are data space areas associated with the system logger address space, IXGLOGR. See DASD-only log stream.
Your installation can use just coupling facility log streams, just DASD-only log streams, or a combination of both types of log streams. The requirements and preparation steps for the two types of log streams are somewhat different; see Preparing to use system logger applications.