Introduction to Data Management

Ensuring Database Consistency With TMF
7-10 15873 Tandem Computers Incorporated
Figure 7-6. TMF Rollforward
S8020-026
Database
Restored to
Latest Possible
Consistent State
Database
Restored
to Earlier
State
Audit
Trails
Online
Dump
Online
Dump
Online
Dump
Audit
Dumps
Rollforward
Processes
The database changes are implemented by the server, at the request of the screen
program run by the TCP. The TCP and server cooperate through the use of
interprocess messages. But it is TMF that locks the affected records. In writing the
server, programmers must follow certain record-locking rules imposed by TMF that
prevent transactions from reading uncommitted changes from other transactions. The
record-locking process is illustrated in Figure 7-7.