Recovery Techniques in
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
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
Overview of the traditional recovery
schemes as well as one of the new
Compares the two, listing the
advantages and disadvantages of
My opinion is that the new recovery
scheme is more efficient to use in
Two main examples are:
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.
The whole log information is
transferred from one base
station to another.
It is fast
It requires a lot of data transfer
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.
There are other traditional
schemes that fall between the
lazy and pessimistic
They have similar advantages
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
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.
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.
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.
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.
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
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.
First situation: the mobile device
uses the data and changes to data
on that base station to recover.
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.
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
In my opinion and after the
comparison, the new scheme is a
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
(ICWMC'06), 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
Environments”, Eighth International Conference on
Parallel and Distributed Systems (ICPADS'01) ,
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
(SRDS'01), October 2001