IMS write-ahead data set (WADS)
The main purpose of the write-ahead data set (WADS) is to contain a copy of committed log records that are in the OLDS buffers, but have not yet been written to the OLDS because the OLDS buffer is not yet full.
IMS uses the WADS to avoid the need to write
partially filled and padded blocks to the OLDS. WADS space is continually
reused after the appropriate log data has been written to the OLDS. If there
is a system failure, IMS uses the log data in the WADS to complete the content
of the OLDS in use, and then closes the OLDS as part of an emergency restart.
This is also an option of the IMS log recovery utility (DFSULTR0). (The
OLDS must be closed before database recovery can take place.) You can change
the following specifications for the WADS at any restart:
- Number of WADSs
- Sequence of WADSs
- WADSs data set names
- Use of single or dual WADSs.