The checkpoint cycle
Although the actual checkpoint cycle consists of a number of reads
and writes, it can be considered to include only four basic phases.
Depending on whether your complex is processing in DUPLEX mode or
DUAL mode (see Checkpoint configuration modes), the actual specifics
of the checkpoint process will vary somewhat; however, the basic processing
is as follows:
- Gaining checkpoint control (and RESERVE for DASD)
- Owning the checkpoint to read and make updates
- Final writing (and RELEASE for DASD)
- Allowing other members access opportunity
As you read the following description of the checkpoint cycle, see Figure 1, which represents a 3-member multi-access spool configuration.
Figure 1. The checkpoint cycle (in
a 3-member multi-access spool environment)