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

Fault-Tolerant Processes
HP COBOL Manual for TNS/E Programs—520347-003
32-15
Concepts
Topics:
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Concepts
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Designing Programs for the TMF Subsystem
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The TMF Subsystem and Requester Screen Transactions
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The TMF Subsystem for Batch Jobs
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Debugging Programs That Use the TMF Subsystem
Concepts
The basic concepts of TMF are:
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Transactions in General
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Multiple-File Transactions
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Multiple Changes to a Single File
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Defining Transactions
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Audit Trails
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Online Dump and Roll-Forward Recovery
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Record Locking
Transactions in General
A transaction is a multistep operation that affects the consistency of a database by
transforming the database from one consistent state to a new consistent state. A
transaction is also a unit of recovery. During a transaction, the database can be
inconsistent. But either the entire transaction must happen, or none of it must happen.
Each transaction has a unique transaction identifier. The identifier includes information
about the starting time of the transaction.
If your transaction involves more than one file or if the single file it involves is available
to other transactions, you can introduce inconsistency into the database.
Multiple-File Transactions
Suppose your process is maintaining a corporate personnel system in which each
department has its own file of information. You want to move an employee’s record
from one file to another. It does not matter whether the process writes the record in the
new file before deleting it from the old file or the reverse. During the interval between
the two events, the database is inconsistent. The employee record is either absent
from the database or present in two places.