Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Recoverability of a File Restoration Process

IP.com Disclosure Number: IPCOM000121535D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 3 page(s) / 100K

Publishing Venue

IBM

Related People

Kinser, CE: AUTHOR [+2]

Abstract

Disclosed is a process which insures that a particular process of restoring a pair of files is recoverable in the case of severe interruption, such as a power outage, while also minimizing the duplication of restoration effort upon resuming.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 48% of the total text.

Recoverability of a File Restoration Process

      Disclosed is a process which insures that a particular
process of restoring a pair of files is recoverable in the case of
severe interruption, such as a power outage, while also minimizing
the duplication of restoration effort upon resuming.

      The restoration procedure, which is not part of this invention,
proceeds as follows. All pertinent data from the first file (file A)
are copied to a temporary file (file tA), with possible
modifications.  All pertinent data from the second file (file B) are
copied to a temporary file (tB), with possible modifications. File B
is deleted, and tB is renamed to become B. File A is deleted and
recreated as empty.  The data from file tA are written record by
record to file A, with possible modifications. (Note that the
restoration of file B is optional.) This invention is to insure that
if this restoration procedure is abnormally interrupted, then it can
be resumed at the latest possible step, and that the data will not be
corrupted.

      Each of the four files contains a validity flag. If the flag is
set, then the data in the file are considered to be reliable;
otherwise, the data are considered to be unreliable. File tA contains
an additional flag which, when set, indicates that the data in both
file tA and file tB are considered to be reliable, regardless of
either file's validity flag setting.

      Each file can exist in one of three states: Nonexistent (N),
Exists-but-Invalid (I), Exists-and-Valid (V). If a file does not
exist, it is in state N. If a file exists and the validity flag is
clear, it is in state I. If a file exists and the validity flag is
set, it is in state V.

      Originally, tA and tB will be in state N. A and B can
independently be in states I or V. (Note that if A or B is in
state I, the data in it are considered to be unreliable. This,
however, is precisely what causes the restoration process to occur,
and is therefore an expected situation.)

      The restoration process with recoverability is as follows:
       1. Consult the table below to determine next step.
       2. The states of A and B are noted, and the files are put in
state I.
       3. tA is created in state I.
       4. Data from A are copied to tA, with possible modifications.
       5. If B is not being restored, steps 6 through 9 are skipped.
       6. tB is created in state I.
       7. Data from B are copied to tB, with possible modifications.
       8. The additional validity flag in tA is set to simultaneously
declare both temporary files valid.
       9. The validity flag in tB is set.
      10. The validity flag in tA is set, and the additional validity
flag is cleared simultaneously.
      11. If B is not being restored, steps 12 through 14 are
skipped.
      12. B is deleted (state N).
      13. tB is renamed to become B (putting tB in state N, and...