Recovery Techniques in Mobile Databases

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24 Νοε 2013 (πριν από 4 χρόνια και 7 μήνες)

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Recovery Techniques in
Mobile Databases

Prepared by Ammar Hamamra


Mobile database system in a way is
a system where the actual database
is stored at one or multiple locations,
but the processing units like laptop,
PDA, cell phones are mobile.

In case of failure, the recovery of the
Mobile Database Systems is far
more complex than the recovery of
the traditional database systems.

Factors that affect the

Geographical Movement


Limited life of batteries

The mobile device might also
break, fall, gets lost, or stolen

Bad connection areas

Network issues like the
weakness of wireless link

Recovery schemes

Overview of the traditional recovery
schemes as well as one of the new
recovery schemes

Compares the two, listing the
advantages and disadvantages of
the schemes

My opinion is that the new recovery
scheme is more efficient to use in
mobile databases

Traditional Schemes

Two main examples are:

lazy scheme

The pessimistic scheme

The Lazy scheme:

The lazy scheme uses the idea of
pointers in the recovery process.

The logs or the changes made to
the data and the recovery
information are stored in base

The lazy scheme

When the mobile node moves from
one base station to another, only the
pointer is stored in the new base
station to refer to the old one.

Advantage: there is very low
overhead on the network.


The large recovery time it needs

More cost and missing deadlines.

Pessimistic scheme

The whole log information is
transferred from one base
station to another.


It is fast


It requires a lot of data transfer

Traditional schemes

The traditional schemes assume
that the mobile unit is going to
recover in the same base station
that it was crashed in.

The traditional schemes do not
consider the highly dynamic
environments such as the
mobile database system.

Traditional schemes

There are other traditional
schemes that fall between the
lazy and pessimistic

They have similar advantages
and disadvantages.

Factors that affect recovery

Failure of the host.

how much the mobile device
moves in a given time.

much information it needs to
communicate with the host.

the size of the message

message gets bigger, it needs
additional power

Factors that affect recovery

Receiving a message is also different
than transmitting a message.

The memory issue

Because a lot of mobile devices are
related to the same base station, the
memory of the base station becomes an
issue trying to save all the recovery
information for all the mobile devices.

Recovery time.

New scheme

States that a good recovery method
is a method that concentrates on the
management and maintenance of
the changes made to the data.

Concentrates on the recovery of the
mobile unit at the time of handoff.

The changes made to data should
be managed to help recover the
mobile unit when it fails.

New scheme

The new system groups together a
set of base stations and calls that a

The new system uses the term
designated Base Station (DBS) to
refer to a station where the mobile
node registers itself with at the first
time in a particular region.

New scheme

Changes made to data by a
particular mobile device are
stored on that DBS.

When the mobile unit moves
from one region to another, it
gets a new DBS.

The changes made to data will
then be transferred from the old
DBS to the new DBS.

New scheme

The new system also requires that
the data should be transferred from
the cache of the mobile device itself
to its DBS.

The new system makes sure that the
mobile device has its own identity,
the identity of the old base station
and the identity of the DBS

New scheme

The new system basically
considers two situations for

The first situation is when the
mobile device recovers in the
same BS where it crashed.

The second situation is the big
advantage that the new system
has over the traditional ones.

New scheme

First situation: the mobile device
uses the data and changes to data
on that base station to recover.

Second situation:

If the mobile device fails in one base
station and then moves to a new base
station and try to recover there, then
identity of the old base station is not
known to the new base station.

New scheme

The old base station notifies the
DBS about the data of the mobile

The new base station then sends
a query to the DBS for information
about the mobile device and the
data that was on it.

Advantages of new scheme

Maintaining the data on the previous
base station so that there is an
updated version incase of recovery.

It avoids multiple copies of data by
deleting a copy when the data gets
transferred to the DBS.

the data gets saved at one central
place for fast recovery which
reduces the recovery time

Disadvantage of new scheme

a lot of the base stations have
the same DBS which means
that the data will be stored on
one DBS that gets overloaded


the recovery process in mobile
databases is more complex than
the recovery in traditional

Two of the main examples on
traditional schemes are the lazy
and pessimistic approaches.


Some of the disadvantages that the
traditional schemes have are high
cost, large recovery time, or large
data transfer.

In my opinion and after the
comparison, the new scheme is a
better scheme.

the mobile node can recover
instantly in case of failure.


Ruchika Dua, Saurabh Bhandari, “Recovery in
Mobile Database System”,
International Conference
on Wireless and Mobile Communications
, July 2006

Sashidhar Gadiraju, Vijay Kumar, “Recovery in the
Mobile Wireless Environment Using Mobile Agents”,
IEEE Transactions on Mobile Computing,
April 2004

Taesoon Park, Namyoon Woo, Heon Y. Yeom, “An
Efficient Recovery Scheme for Mobile Computing
Eighth International Conference on
Parallel and Distributed Systems (ICPADS'01)
June 2001

T. Park, N. Woo, H. Yeom, “Efficient Recovery
Information Management Schemes for the Fault
Tolerant Mobile Computing Systems”,
20th IEEE
Symposium on Reliable Distributed Systems
, October 2001