Browse Prior Art Database

Algorithm for Determining an Optimal Recovery Strategy

IP.com Disclosure Number: IPCOM000104924D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Schwendemann, W: AUTHOR [+2]

Abstract

The amount of time needed to recover a database can vary depending upon which recovery model is chosen - "net change" or "full" technique. This algorithm gives an installation a quantitative way of deciding which recovery technique to use.

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

Algorithm for Determining an Optimal Recovery Strategy

      The amount of time needed to recover a database can vary
depending upon which recovery model is chosen - "net change" or
"full" technique.  This algorithm gives an installation a
quantitative way of deciding which recovery technique to use.

Two Definitions of Recovery Techniques are:

o   Full Recovery of the database proceeds by processing "log
    tape(s)" in a chronological fashion (i.e., old to new).  The log
    records on each tape are also arranged in the same sequence).
    When a log record is read, the "after image" in the log record is
    applied to the "before image" of the database record.  Recovery
    is complete when all the log tape(s) have been processed.
o     Net Change Recovery of the database proceeds by processing "log
    tape(s)" in a reverse chronological fashion (i.e., new to old.
    The log records on each tape are also arranged in the same
    sequence).  When a log record is read, a check is performed to
    determine if this record (check is based on record identifier,
    i.e., RID) has already been processed.  If it has, the log record
    is discarded and the next log record or tape is processed.
    Otherwise, the "after image" in the log record is applied to the
    "before image" of the database record.  Recov ery is complete
    when all the log tape(s) have been processed.

Algorithm for Choosing Optinal Recovery Technique - Assumptions

o   database conforms to 80/20 rule.  Eighty percent of the updates
    apply to only twenty percent of the database.  The updates are
    uniformly distributed.
o   the "path length" (i.e., number of instructions executed) of
    applying a log record and determining whether a RID has already
    been applied can be quantified.

N                           number of records database is comprised
of

M                           total number of log records

COST_CHECK_RID              the processed cost associated with
                            determining whether a log record with the
                            same RID has already been applied...