Recovery Techniques in Mobile Databases Prepared by Ammar Hamamra

Recovery Techniques in Recovery Techniques in Mobile DatabasesMobile Databases

Prepared by Ammar HamamraPrepared by Ammar Hamamra

IntroductionIntroduction

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

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

Factors that affect the Factors that affect the recovery:recovery:

Geographical MovementGeographical Movement DisconnectionDisconnection Limited life of batteriesLimited life of batteries The mobile device might also The mobile device might also

break, fall, gets lost, or stolenbreak, fall, gets lost, or stolen Bad connection areasBad connection areas Network issues like the Network issues like the

weakness of wireless linkweakness of wireless link

Recovery schemesRecovery schemes

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

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

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

Traditional SchemesTraditional Schemes

Two main examples are:Two main examples are: lazy schemelazy scheme The pessimistic schemeThe pessimistic scheme

The Lazy scheme: The Lazy scheme: The lazy scheme uses the idea of The lazy scheme uses the idea of

pointers in the recovery process.pointers in the recovery process. The logs or the changes made to The logs or the changes made to

the data and the recovery the data and the recovery information are stored in base information are stored in base stations. stations.

The lazy schemeThe lazy scheme

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

Advantage: there is very low Advantage: there is very low overhead on the network.overhead on the network.

Disadvantages:Disadvantages: The large recovery time it needsThe large recovery time it needs More cost and missing deadlines.More cost and missing deadlines.

Pessimistic schemePessimistic scheme

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

Advantage:Advantage: It is fastIt is fast

Disadvantage:Disadvantage: It requires a lot of data transfer It requires a lot of data transfer

Traditional schemesTraditional schemes

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

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

Traditional schemesTraditional schemes

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

They have similar advantages They have similar advantages and disadvantages.and disadvantages.

Factors that affect recoveryFactors that affect recovery

Failure of the host.Failure of the host. how much the mobile device how much the mobile device

moves in a given time.moves in a given time. much information it needs to much information it needs to

communicate with the host.communicate with the host. the size of the message the size of the message

transmitted.transmitted. message gets bigger, it needs message gets bigger, it needs

additional poweradditional power

Factors that affect recoveryFactors that affect recovery

Receiving a message is also different Receiving a message is also different than transmitting a message.than transmitting a message.

The memory issueThe memory issue Because a lot of mobile devices are Because a lot of mobile devices are

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

Recovery time. Recovery time.

New schemeNew scheme

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

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

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


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

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


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

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

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


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

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


The new system basically The new system basically considers two situations for considers two situations for recovery.recovery.

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

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


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

Second situation:Second situation: If the mobile device fails in one base If the mobile device fails in one base

station and then moves to a new base station and then moves to a new base station and try to recover there, then station and try to recover there, then identity of the old base station is not identity of the old base station is not known to the new base station. known to the new base station.


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

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

Advantages of new schemeAdvantages of new scheme

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

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

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

Disadvantage of new schemeDisadvantage of new scheme

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

ConclusionConclusion

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

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

ConclusionConclusion

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

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

the mobile node can recover the mobile node can recover instantly in case of failure.instantly in case of failure.

ResourcesResources

Ruchika Dua, Saurabh Bhandari, “Recovery in Ruchika Dua, Saurabh Bhandari, “Recovery in Mobile Database System”, Mobile Database System”, International Conference on Wireless and Mobile CInternational Conference on Wireless and Mobile Communications (ICWMC'06)ommunications (ICWMC'06), July 2006, July 2006

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

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

T. Park, N. Woo, H. Yeom, “Efficient Recovery T. Park, N. Woo, H. Yeom, “Efficient Recovery Information Management Schemes for the Fault Information Management Schemes for the Fault Tolerant Mobile Computing Systems”, Tolerant Mobile Computing Systems”, 20th IEEE Symposium on Reliable Distributed Syst20th IEEE Symposium on Reliable Distributed Systems (SRDS'01)ems (SRDS'01), October 2001 , October 2001

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Recovery Techniques in Mobile Databases Prepared by Ammar Hamamra