Introduction to Data Management

Ensuring Database Consistency With TMF
15873 Tandem Computers Incorporated 7-3
Figure 7-1. TMF Transaction Backout
S8020-021
ACCEPT INPUT
.
BEGIN TRANSACTION
.
.
SEND REQUEST
TO SERVER
.
.
.
END TRANSACTION
READ REQUEST
.
.
.
UPDATE
DATABASE
.
.
.
REPLY TO
REQUEST
Requester Server
User
Add new
employees
Transaction
aborts!
Database changes
associated with
transaction are
backed out
Audit Trails
Transaction backout is made possible by the use of audit trails. An audit trail is a file
in which TMF maintains information about transactions, including images of records
before and after each transaction takes place, and logging information about events
related to each transaction.
You can designate any or all of the files in your database as an audited file; then, any
write or update operation on that file will be recorded in an audit trail. When the
transaction updates a record in the database, TMF writes the before and after images
of that record to the audit trail before it commits the transaction to the database. This
procedure is shown in Figure 7-2.