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Recovery Techniques in Mobile Databases

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					Recovery Techniques in
  Mobile Databases

     Prepared by Ammar Hamamra
Introduction

   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
recovery:
   Geographical Movement
   Disconnection
   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
      stations.
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.
   Disadvantages:
       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.

   Advantage:
       It is fast
   Disadvantage:
       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
    approaches.

   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
    transmitted.
       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
    region.

   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
    recovery.
   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
   device.
  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
    sometimes.
Conclusion

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

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

   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.
Resources
   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) ,
    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
    (SRDS'01), October 2001
Questions?

				
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