Availability Guide for Application Design

Data Protection and Recovery
Availability Guide for Application Design—525637-004
4-2
What Is a Transaction?
having to deal with complex checkpointing operations. In addition, the product itself is
designed to be highly available by allowing online reconfiguration and tolerance of
error conditions.
TMF sustains high performance in transaction-processing applications. To support
transaction-processing applications, TMF can manage thousands of complex
transactions sent by hundreds of users to a common database through multiple
interfaces. The database can be distributed among many disks on a system and
across many HP systems in an Expand network. The database can be a NonStop
SQL/MP relational database, an Enscribe database, or a combination of both.
TMF manages transactions submitted to a database from terminals, workstations, and
other devices such as point-of-sale equipment.
This subsection discusses the properties of a TMF transaction and how transactions
are coordinated. It shows how concurrent access to data can be made without
compromising data integrity.
Database Recovery on page 4-6 describes how TMF features protect your data
against system or component failure or during operator action. APIs to Transaction
Facilities on page 4-9 provides an overview of the programmatic interfaces.
For more information about TMF, refer to the following publications:
•
The TMF Introduction provides a complete overview of TMF.
•
The TMF Application Programmer’s Guide provides information on how to write
TMF applications using the Transaction Management Facility (TMF) programmer
interface.
•
The TMF Operations and Recovery Guide and the TMF Configuration and
Planning Guide can be used to reconfigure TMF without bringing your application
down.
What Is a Transaction?
A transaction is a sequence of one or more operations used to perform a single task.
Its scope starts at the program statement that starts the transaction and finishes at the
program statement that finishes the transaction, usually by confirming the changes
made or by rolling back those changes. Each transaction has the following properties:
•
It is atomic.
Either all of the transaction takes place or none of it does.
•
It is consistent.
The combined actions of the transaction must not violate any integrity constraints.
•
It is isolated and can be serialized.