The physical structure of the log

The active log consists of VSAM data sets with certain required characteristics.

The physical output unit written to the active log data set is a control interval (CI) of 4096 bytes (4 KB). Each CI contains one VSAM record.

Physical and logical log records
The VSAM control interval (CI) provides 4089 bytes to hold DB2 information. That space is called a physical record. The information that is to be logged at a particular time forms a logical record, whose length varies independently of the space that is available in the CI.
The log record header
Each logical record includes a prefix, called a log record header (LRH), which contains control information.
The log control interval definition (LCID)
Each physical log block, also referred to as a control interval, includes a suffix called the log control interval definition (LCID), which tells how record segments are placed in the physical control interval.
Log record type codes
The type code of a log record tells what kind of DB2 event the record describes.
Log record subtype codes
The log record subtype code provides a more granular definition of the event that occurred and that generated the log record. Log record subtype codes are unique only within the scope of the corresponding log record type code.
Interpreting data change log records
For specific log record types, DB2 provides the mapping and description that you can use to interpret data changes that are made to DB2 tables from the log.

Parent topic: Reading log records