Protecting Against Data Loss
The following sections discuss how system interruptions and hardware failure are handled.
If a transaction build-up is interrupted by a system failure or a program termination (deliberate or otherwise) the transaction is aborted and none of the requested changes are made to the database.
Transactions which are interrupted after the request to commit, but before all operations in the transaction have been executed on the database, are completed by the automatic recovery functionality when the databank involved is next accessed. There is no possibility of transaction conflict in such an automatic completion, since no other process can access the affected data as long as an incomplete transaction is pending.
In the event of a system failure that interrupts one or more application programs, it may be necessary to manually examine the database contents to determine which transactions failed to commit before the interruption.
A databank that is damaged by hardware failure (e.g. a disk crash) may be recovered using back-up copies and the transaction log (
LOGDB), provided that all write operations on the databank have been logged (and that the back-up copies and the
LOGDBdatabank are intact).
Backup and restore facilities are described in the Mimer SQL System Management Handbook.
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