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Browse Prior Art Database

Incremental Check-Point Copy with Rapid Check-Point Reconstruction

IP.com Disclosure Number: IPCOM000115812D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 99K

Publishing Venue

IBM

Related People

Ouchi, NK: AUTHOR

Abstract

Disclosed is a mechanism that permits incremental copying of changed data for a check-point copy while providing rapid reconstruction of any given check-point copy. Also disclosed is a mechanism that permits keeping the most recent N check-points.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Incremental Check-Point Copy with Rapid Check-Point Reconstruction

      Disclosed is a mechanism that permits incremental copying of
changed data for a check-point copy while providing rapid
reconstruction of any given check-point copy.  Also disclosed is a
mechanism that permits keeping the most recent N check-points.

      Data are divided into pages where changed pages are
periodically copied to a structure of previously copied pages so that
a check-point can be rapidly reconstructed from these incremental
copies.

      Data processing disciplines to recover from hardware, software,
and operations failures include the use of making a copy of a data
base and a journal of subsequent transactions so that the data base
can be recreated to a specific transaction.  This requires that the
data base be copied on a periodic basis to limit the length of the
journal and bound the journal space and time needed to recreate the
data base using the journal.  However, the time required to make the
copy of the data base can be large for large data bases.  Mechanisms
to make virtual copies of the data base thru the use of pointers have
been disclosed.

      The concept of copying only data that have changed has been in
use in the art.  This has reference as "incremental" check-point
copies.  This requires the need of indicators as to change since the
last incremental check-point.  However, the resulting set of
incremental check-points can be thought of as another form of journal
and can require an extensive processing to recreate the data base to
a specific transaction.

      Disclosed is a mechanism where the data are divided into
elements and pages, where the incremental copies of the pages are
kept in a stack for each page frame.  This is illustrated in the top
of Fig. 1 where the incremental copies of each page frame are kept in
the area called CHECK-POINTS, the active data are in the page frames
called ACTIVE, and FLAGs are used to indicate if the page frame had
changed since the last incremental check-point.  The various
che...