Types of log streams

You must define log streams in data sharing and non-data sharing environments.

The type of log stream that you define depends on whether you access the log stream from one LPAR or from multiple LPARs.
  • If you only access a log stream from one LPAR, you can use a DASD-only log stream or you can use a coupling facility log stream.
  • If you access a log stream from more than one LPAR, you need a data sharing environment and a coupling facility log stream.

In a data sharing environment, you must define log streams in a coupling facility to enable logging operations to access the same log stream across all participating logical partitions (LPARs) in the sysplex. Multiple LPARs can generate inserts, updates, and deletes to the same VSAM data set. The target CICS® region can write changes from all LPARs in the correct order and maintain transactional consistency.

For example: CICS updates all source files from one LPAR (LPAR1). The source server runs on a different LPAR (LPAR2). In this case, you need a coupling facility log stream.

A data sharing environment also requires that all the systems that access the source files share an ICF catalog.

For DASD-only log streams, all applications and the source server must run on the same image. If you have to apply maintenance, you might incur a replication outage.

For additional guidance about setting up log streams in a coupling facility, which type of log stream to define, and sizing the log streams, see the CICS product documentation about defining the logger environment.