System log data set
IMS uses the SLDS in both the online and batch environments. In the online environment, an SLDS contains archived OLDS data. In the batch environment, an SLDS contains current log data.
Each execution of the Log Archive utility creates an SLDS. One SLDS can contain data from one or more OLDSs. You use an SLDS as input to the database recovery utilities (Database Recovery, Database Change Accumulation, and Batch Backout). You can also use an SLDS during an emergency restart of IMS. SLDSs can be stored on DASD, tape, or other mass storage.
DBRC maintains information about SLDSs in the RECON data set:
- For batch subsystems, DBRC maintains SLDS information in the PRILOG and SECLOG records.
- For online subsystems, DBRC maintains SLDS information in the PRILOG and SECLOG records only if you do not specify an RLDS when you run the Log Archive utility. Otherwise, DBRC maintains SLDS information in PRISLD and SECSLD records.
The Log Archive utility tells DBRC which OLDS it is archiving and which SLDS it is creating. The IMS online system can reuse OLDSs that have been archived.
Generally, you want to copy all the log records from the OLDS to the SLDS, but you can specify specific records. If you want to omit some types of log records from the SLDS in order to save space, include the NOLOG keyword when you run the Log Archive utility. The SLDS must always contain those records that might be needed for database recovery, batch backout, or IMS restart. The records that you can omit are:
- X'10'
- Security violation records
- X'45'
- Statistics records written during checkpoint
- X'5F'
- Call trace record
- X'67'
- Communications (SNAP) trace records
- X'69'
- Unauthorized ID record (for 3275 display terminal)
IMS dynamically allocates an SLDS during IMS restart whenever log data required for restart read processing is not available from an OLDS. The OLDS might be unavailable because it has been archived, and because one of the following is true:
- The OLDS has been reused.
- The PRIOLDS and SECOLDS records have been deleted from the RECON data set.
To allow IMS to dynamically allocate SLDSs, you must specify the SLDS device type Dynamic Allocation macro (DFSMDA). DBRC provides the data set name and volume information required for dynamic allocation.