COBOL Manual for TNS/E Programs (H06.08+, J06.03+)

CHECKPOINT defines a restart point for the backup process of a process pair and transfers the
information that the backup requires to restart.
data-name-1
is the name of a data item to checkpoint, typically an item used for an I-O transfer of data that
is relevant to the current state of the program and is needed if the backup process is to continue
the operation in the event of a failure. data-name-1 cannot be a BASED item.
FILE
indicates that the next data item is the name or number of a file.
data-name-2
is an integer, the operating system file number of the file whose sync block is to be checkpointed.
Use data-name-2 only when files are managed entirely with ENTER statements that call TAL
routines (rather than COBOL I-O statements).
file-name
is the name of a file (usually a disk file) whose sync block is to be checkpointed.
QUEUE
indicates that the next data item is the name of a checkpoint list.
checkpoint-list-name
is the name of a checkpoint list containing information that must be transferred to the backup
process. The checkpoint list is a COBOL record with a specific structure in which the message
changes are recorded. The information is returned by these Saved Message Utility (SMU)
routines:
PUTPARAMTEXTDELETESTARTUPALTERPARAMTEXT
PUTSTARTUPTEXTPUTASSIGNTEXTDELETEASSIGN
PUTASSIGNVALUEDELETEPARAM
For information on SMU routines and a description of the checkpoint list record, see Saved Message
Utility (SMU) Overview (page 612).
Usage Considerations:
• Reason to Checkpoint
If a backup process takes over, the contents of items that are not checkpointed are undefined.
• Conditions Under Which Data Items Are Checkpointed
The compiler checkpoints only those data items that one or more CHECKPOINT statements
specify explicitly. These data items can be in either the Working-Storage Section or the
Extended-Storage Section.
• Sending Values to a Backup Process
When CHECKPOINT executes, the values of the data items and file sync blocks are sent to
the fault-tolerant facility in the backup process. If the primary process fails before another
CHECKPOINT 303