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
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SQL/MX Requirements for TMF
TMF handles backout operations without operator intervention by using the audit trails
automatically cycled by TMF. The TMF backout process uses before-images in audit
trails to undo the effects of an aborted transaction.
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 after-
images 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.
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