The document discusses recovery in mobile database systems. It outlines a proposed recovery scheme where the first base station a mobile user registers with in a region is designated as the base station for storing the user's log entries. When the user moves between regions, the designated base station transfers the log to the new region's designated base station, allowing for efficient recovery when failures occur. The scheme aims to reduce recovery time for mobile users.

1. Recovery in
Mobile
Database
System
Presented by:
PRAVEEN PALLAV
(1DS09IS061)
ISE - DSCE - 2013 1

2. RECOVERY IN MOBILE DATABASE SYSTEM
Outline
 Introduction
 Previouswork
 System model
 Recovery and its issue
 Proposed recovery scheme
 Advantages
 Disadvantages
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3. RECOVERY IN MOBILE DATABASE SYSTEM
Introduction
 Aim to provide a scheme which will help
a MU recover efficiently, taking reduced
amount of time to recover from its last
secure state
 This new mobile computing environment
poses challenging problems in designing
fault-tolerant systems
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4. RECOVERY IN MOBILE DATABASE SYSTEM
Motivation
 Telecommunication services need to improve the
quality, availability, and reliability of cellular services.
 information accessing capability regardless of the location
 Motivated by such growing demand, we envision an
information processing system
 Need of fault-tolerant systems which suit the mobile
environment
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5. RECOVERY IN MOBILE DATABASE SYSTEM
Previous work
 Lazy schemes
 Pessimistic scheme
 Schemes based on the MU’s movement
 Distance based
 Frequency based
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6. RECOVERY IN MOBILE DATABASE SYSTEM
System model
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7. RECOVERY IN MOBILE DATABASE SYSTEM
Problem Specifications
 Location is not fixed
 Batteries have limited power
 Different types of failures
 Hard failure
 Soft failure
 Weak wireless link
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8. RECOVERY IN MOBILE DATABASE SYSTEM
Recovery
A mechanism to restore an intermediate
consistent state of the system.
 made possible by maintaining log
 log management should be very efficient
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9. RECOVERY IN MOBILE DATABASE SYSTEM
…….
 Appropriate recovery strategy needs to
be chosen
 Failure rate
 Memory constraints
 Recovery time
 Communication / Mobility Ratio
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10. RECOVERY IN MOBILE DATABASE SYSTEM
 Recovering the MU state on its failure
at the time of handoff
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11. RECOVERY IN MOBILE DATABASE SYSTEM
Key terms
 Region: BSs under the same MSC.
 Designated BS: First BS for a MU registration
inside a region.
MSC
BS1 BS3
BS2
DBS
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12. RECOVERY IN MOBILE DATABASE SYSTEM
………
 Characteristics of DBS:
 Store all the log entry done by respective
MU.
 Different DBS for different region.
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13. RECOVERY IN MOBILE DATABASE SYSTEM
Inter-region
 Step 1: MU registers with a BS in a Region, changes
state of that BS as DBS for that MU.
 Step 2: MU does some transactions, stores the log
at respective DBS.
 Step 3: MU goes out of that region and comes
under another region and repeats the same
registration procedure, making first registered BS as
DBS for that region.
 Step 4: Current DBS calls for the logs from the
previous region DBS.
 Step 5: Previous DBS transfers all the respective MU
log to the new DBS.
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14. RECOVERY IN MOBILE DATABASE SYSTEM
Inter-region
MSC MSC
BS1 BS3 BS1 BS3
DBS
BS2 DBS
BS2
LOG
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15. RECOVERY IN MOBILE DATABASE SYSTEM
Intra-region
 Log transfer from MU cache to BS:
 When?
 EitherMU memory is exhausted.
 Or a handoff is detected.
 How?
 Log is updated to the current BS.
 It is appended to the DBS log.
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16. RECOVERY IN MOBILE DATABASE SYSTEM
Log management
 Registration:
 Connect(MHID, PBSID, DBSID)
 MHID: ID of the MU.
 PBSID: Previous BS’s ID.
 DBSID: ID of respective region’s DBS.
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17. RECOVERY IN MOBILE DATABASE SYSTEM
Case 1 log management
 Step 1: MU registers with a BS in a Region, changes
state of that BS as DBS for that MU.
 Step 2: MU does some transactions, stores the log at
respective DBS.
 Step 3: MU goes out of DBS vicinity and comes under
BS2 cell.
 Step 4: MU registers itself to new BS with
connect(MHID, PBSID, DBSID).
 Step 5: BS2 sends a message to PBSID ‘MHID is with
me’.
 Step 6: Since the PBS is also the DBS for that
MU, hence no action taken and the message is
discarded.
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18. RECOVERY IN MOBILE DATABASE SYSTEM
Case 1 log management
MSC
DBS
BS1 BS3
MHID is with me
BS2
Connect(MHID, PBSID, DBSID)
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19. RECOVERY IN MOBILE DATABASE SYSTEM
Case 2 log management
Going on in addition with previous scenario:
 Step 1: Now MU has moved from BS2 to BS3,
repeats the same registration process as in
previous case and the PBS (BS2) is notified by
the current BS (BS3) about that MU existence.
 Step 2: Now BS2 checks for the PBS for that
MU in its memory, since the PBS is the DBS
hence no delete message or action required.
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20. RECOVERY IN MOBILE DATABASE SYSTEM
Case 2 log management
MSC
MHID is with me
DBS
BS1 BS3
Since previous BS is DBS, hence no
BS2
delete message is send Connect(MHID, PBSID, DBSID)
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21. RECOVERY IN MOBILE DATABASE SYSTEM
Case 3 log management
In addition with previous scenario:
 Step 1: MU goes from BS3 to BS4 now and performs
the same registration process with BS4, BS4 notifies
BS3 about MU.
 Step 2: The with respect to that MU, PBSID stored at
BS3 is not the DBS hence a ‘delete’ message from
BS3 is sent to BS2.
 Step 3: BS2 on receiving of ‘delete’ message transfers
all log for that MU to the respective DBS.
 Step 4: DBS acknowledges BS2 about log successful
transfer.
 Step 5: BS2 deletes respective MU’s log entry from its
memory.
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22. RECOVERY IN MOBILE DATABASE SYSTEM
Case 3 log management
MSC
MHID is with me
BS4
DBS
Acknowledgement
Delete Connect(MHID, PBSID, DBSID)
BS3
BS2
Delete LOGS entry
the log
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23. RECOVERY IN MOBILE DATABASE SYSTEM
Case 4 log management
When we further move on in this scenario:
 Step 1: MU comes back to the recent visited BS
forming a loop i.e. from BS4 to BS3, registration
process is done in the same previous manner.
 Step 2: BS4 checks whether the PBS and current BS
of that MU in its memory are same? If yes, send the
respective MU’s log to current BS i.e. logs are
transferred from BS4 to BS3.
 Step 3: BS3 appends the BS4 log with its current
available log and BS3 deletes the PBSID for that MU
from its memory.
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24. RECOVERY IN MOBILE DATABASE SYSTEM
Case 4 log management
MSC
PBSID==
BS4
DBS LOGS?
CBSID
MHID is with me
Append with previous
BS3
Log & delete the PBSID.
Connect(MHID, PBSID, DBSID)
BS2
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25. RECOVERY IN MOBILE DATABASE SYSTEM
Recovery case 1
 Recovery in same BS where it crashed:
 Uses log saved in current BS.
 If not sufficient go for previous BS.
 If that is also insufficient, go for MU’s DBS.
 By using DBS log MU is restored with
required previous state.
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26. RECOVERY IN MOBILE DATABASE SYSTEM
Recovery case 2
 Recovery in BS other than in which failed:
 Current BS unaware of handoff.
 PBSID is unavailable.
 Old BS in which MU failed notifies respective
DBS about MU failure.
 When MU tries to recover, current BS queries
DBS for log.
 Using DBS log MU is recovered.
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27. RECOVERY IN MOBILE DATABASE SYSTEM
Advantages
 Preceding BS log maintenance gives
latest recovery option.
 Unification at DBS avoids redundancy of
logs.
 Loop is tackled.
 Auto unification of logs at one site helps:
 Quick recovery.
 Achieve real time system deadlines.
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28. RECOVERY IN MOBILE DATABASE SYSTEM
Disadvantage
 DBS with many MUs gets overburdened.
 Single point of failure.
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29. RECOVERY IN MOBILE DATABASE SYSTEM
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