Recovering from Aborts During Backup

An abnormal failure can occur during a filesave for a number of reasons: a bug in the user’s program, a Group Format Error, entering a CTRL+BREAK, etc. How the user recovers from such a failure depends on whether or not the Z option of the SAVE command was used in the filesave. The FILE-SAVE Proc uses SAVE with the Z option.

The SAVE command with the Z option clears the Group Update Flag of each group as it is saved. The base frame ID of each saved group is stored in a table which is used to reset the Group Update Flags should an abnormal abort occur during the filesave. If a filesave aborts, how you recover from the abort determines the type of save you will subsequently be able to perform after the recovery.

A system-wide flag called the full filesave required flag is set at the beginning of each SAVE operation that uses the Z option. This flag inhibits further incremental filesaves until either the filesave successfully finishes, the Group Update Flags are reset after an abort, or a full filesave is performed with FILE-SAVE.

Recovery Methods

If the Z option was not used, no Group Update Flags were cleared, so you can restart the filesave immediately. If the Z option was used, the cleared flags for the groups that were saved can be restored to their pre-backup state if necessary, as long as the frame ID table has been preserved. If for any reason the frame ID table has been lost, you cannot perform any incremental filesaves, since the Group Update Flags are in an invalid state and cannot be reset.

When a filesave aborts, you will enter the Virtual Debugger (indicated by the ! prompt).

If You Enter the Debugger

At the ! prompt, type END if you want to reset cleared update flags to their pre-backup state. The following message displays:

RESETTING ZEROED UPDATE FLAGS -- WAIT

Resetting flags can take considerable time on large systems. (To interrupt the resetting procedure at any time, press CTRL+BREAK, then type OFF at the ! prompt to return to system level.) When the resetting procedure is finished, the TCL prompt appears. Do another filesave as soon as possible.

If the next filesave is a full filesave, type OFF at the ! prompt. This deletes the frame ID table. You cannot do an incremental filesave once the frame ID table is deleted.