SQL/MX 3.2.1 Management Manual (H06.26+, J06.15+)

Volume Recovery
Volume recovery recovers the database in the event of a disk crash or system failure. When TMF
is restarted after a failure, volume recovery is initiated automatically for each accessible data
volume on the system (except for volumes explicitly disabled in TMF).
To recover the files, the volume recovery process reapplies committed transactions to ensure they
are reflected correctly in the database, and then backs out all transactions that were incomplete
at the time of the interruption.
File Recovery
File recovery reconstructs specific audited files when the current copies on the data volume are not
usable; for example, if a system or media failure jeopardizes the consistency of one or more audited
files. A file could require file recovery for one or more reasons, including:
• A disk failure (irreparable media failure) occurs.
• A volume or system failure occurs, and volume recovery cannot recover the file.
• A file is mistakenly dropped.
• An application program incorrectly changes the database.
File recovery includes restoring online dumps from tape to disk, applying the afterimages from the
audit trail to the database records, and then backing out all transactions that were incomplete at
the time of the system interruption or failure.
NonStop SQL/MX Requirements for TMF
TMF audits all SQL/MX files (including the files created for tables, indexes, and views) to ensure
both the integrity of the database and timely recovery from media failures or incomplete transactions.
As a general rule, TMF must be available when users are running SQL/MX application programs
or using MXCI. In particular, TMF is required for:
• DDL statements.
• SQL/MX compilations, whether explicit or requested interactively through MXCI or through
dynamic SQL/MX applications.
• DML statements performing INSERT, UPDATE, or DELETE operations on tables or views.
• SELECT statements not using BROWSE ACCESS on tables or views.
Some previously compiled programs or previously prepared DML statements execute successfully
when TMF is unavailable if the statements do not require TMF transactions. These DML statements
include queries (SELECT statements or cursor operations) that specify BROWSE access on tables
and views.
Nevertheless, even these queries and statements fail if automatic recompilation is required (for
example, if an object in the access path becomes unavailable).
Guidelines for Configuring TMF
Before you install NonStop SQL/MX, the appropriate product version of TMF must be installed,
configured correctly, and active for transaction processing on a system. The guidelines discussed
next apply to configuring TMF for use with NonStop SQL/MX.
Determining a Level of Data Protection
Configure TMF for the level of protection your application needs. The minimum level of protection
uses the automatic recovery features of TMF backout and volume recovery. Audit dumps and online
dumps allowing file recovery are optional.
50 Planning Database Security and Recovery