SQL/MX 2.x Installation and Management Guide (G06.24+, H06.03+)

Planning Database Security and Recovery
HP NonStop SQL/MX Installation and Management Guide—523723-004
5-10
Using TMF for Transaction Recovery, Database
Consistency, and Database Recovery
Using TMF for Transaction Recovery,
Database Consistency, and Database
Recovery
TMF protects SQL/MX databases by managing database transactions, monitoring
database activity through the use of audit trails, and enabling database recovery.
TMF Concepts
The use of TMF requires an understanding of these TMF elements:
•
Transactions
•
Audit trails
•
Audit files
•
Audit dumps
•
Online dumps
A brief overview of these elements follows. For more information, see the TMF
Planning and Configuration Guide.
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/MX operations are called TMF transactions because TMF
manages these transactions.
A TMF transaction can span numerous database changes that affect multiple files on
multiple disk volumes and nodes. TMF can abort an incomplete transaction if a failure
occurs during the transaction to ensure consistency. Either all or none of the changes
in a transaction are applied to the database. During normal processing, TMF 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, TMF 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 TMF records information about transaction 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