SQL/MP Installation and Management Guide

Planning Database Security and Recovery
HP NonStop SQL/MP Installation and Management Guide—523353-004
4-10
The TMF Subsystem
The TMF Subsystem
The TMF subsystem provides transaction protection, database consistency, and
database recovery.
TMF Concepts
Use of the TMF subsystem requires an understanding of these TMF elements:
•
Transactions
•
Audit trails
•
Audit files
•
Audit dumps
•
Online dumps
These paragraphs give a brief overview of these elements; for more information, see
the TMF Introduction.
Transactions
A transaction, in general, is a multistep operation with a designated beginning and end
that changes a database. For example, a transaction for an airline reservation could
include the operations of adding a reservation to the airline passenger list, issuing a
ticket, and adding the ticket price to the accounts receivable table. Transactions
associated with SQL/MP operations are called TMF transactions.
A TMF transaction can span numerous database changes that affect multiple files on
multiple disk volumes and nodes. The TMF subsystem can abort an incomplete
transaction if a failure occurs during the transaction, thus ensuring consistency—either
all or none of the changes in a transaction are applied to the database. During normal
processing, the TMF subsystem also maintains the necessary locks on data to ensure
consistency of the database.
Audit Trails
If a system, disk, or program fails during a transaction, the TMF subsystem uses audit
trails to restore the files to their original state before the start of the transaction. Each
audit trail is a series of files in which the TMF subsystem records information about
transactions’ changes to a database. The information includes:
•
Before-images, which are copies of data records before a transaction changes
them
•
After-images, which are copies of the changed records