The log stream
A log stream is an application specific collection of data that is used as a log. The data is written to and read from the log stream by one or more instances of the application associated with the log stream. A log stream can be used for such purposes as a transaction log, a log for re-creating databases, a recovery log, or other logs needed by applications.
- Interim storage, where data can be accessed quickly without incurring the overhead of 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 offloaded to DASD log data sets.
- 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 Setting up the system logger configuration.
- The location and concurrent activity of writers and readers to a log stream's log data
- The volume of log data written to a log stream.
- You require more than one concurrent log writer or log reader to the log stream from more than one system in the sysplex.
- You are recording high volumes of log data being to the log stream.
- You require no more than one concurrent log writer or log reader to the log stream from more than one system in the sysplex.
- You are recording low volumes of log data to the log stream.
With z/OS® Release 3 and higher, you can also upgrade existing coupling facility log streams to use a different coupling facility structure. See Updating an existing structure-based log stream to another structure.