TMF Application Programmer's Guide (G06.24+)

Designing Single-Threaded Processes

HP NonStop TMF Application Programmer’s Guide—522419-004

2-6

Checkpointing Strategy

Within the TMF programming environment, requesters can be coded as NonStop

process pairs so that the backup process will take over automatically if the primary

process should fail.

A full discussion of the design of NonStop process pairs is beyond the scope of this

manual. The topics that follow do, however, present some requirements that TMF

imposes upon the use of checkpoints and a strategy for the most effective placement

of checkpoints within the primary requester process.

The Transaction Pseudofile (TFILE)

Every TMF requester process has its own transaction pseudofile, called a TFILE. The

TFILE is not a physical I/O device file; it is never the target of actual I/O operations.

Instead, the TFILE’s access control block (ACB) serves as a mechanism whereby TMF

can represent the state of transactions in a form that resembles a file.

Each entry in a TFILE corresponds to a single transaction and includes the transaction

identifier and a status descriptor. The status descriptor is used at the completion of the

transaction to indicate whether the transaction was committed or aborted.

For single-threaded requesters, the TFILE has only one entry: when the primary

requester process issues a BEGINTRANSACTION call, the entry in the TFILE for the

preceding transaction is overwritten by the information about the new transaction.

For single-threaded requesters that are not using checkpoints, the file system

automatically creates a TFILE that contains one entry when the requester first calls

BEGINTRANSACTION. Such requesters can ignore the existence of the TFILE

altogether.

If a requester is the primary process of a NonStop process pair, however, it must

explicitly open the TFILE and then execute a CHECKOPEN call to create the backup

requester’s copy of the TFILE.

96 Transaction duration surpassed autoabort timeout interval

97 One of the following occurred:

•

Application requested abort

•

File system initiated abort

•

Server process involved in transaction failed

•

Unknown miscellaneous error occurred

1116 NonStop SQL/MP subsystem initiated abort

Table 2-2. Unilateral Abort Error Numbers (page2of2)

Number Cause of Error