1. Implementation and Evaluation of Delay-Aware and Fault-Tolerant Mobile Transactions
Brahim Ayari, Abdelmajid Khelil, Neeraj Suri and Eugen Bleim
Department of Computer Science
TU Darmstadt, Germany
{brahim, khelil,

2. Database Use in Healthcare
Mobile Healthcare
Life assist systems
Patient data management
Body area network
Mobile Database
Mobile participants
Strict data consistency
Atomic commit is a
fundamental operation
Patient
records
Wired Network

3. Objectives Ensure strict atomicity
Minimize the blocking time of resources in the wired network
Minimize transaction abort rate (heterogeneity and fault-tolerance)
Reduce (wireless) message complexity
System Model
Related Work
FT-PPTC Approach
Implementation
Measurements
Summary

4. System and Fault Model Heterogeneity Perturbations Wireless networks
Mobile nodes
Slowest process determines
resource blocking time
Perturbations
Disconnections
Node/Comm failures
Increases resource
blocking time
or abort rate
Wired Network
WLAN
GPRS
UMTS

5. Related Work Unilateral Commit for Mobile (UCM) [PDCS’00]
Supports mobile participants
Strict assumptions (two-phase locking for all participants)
Mobile Two Phase Commit (M-2PC) [ADC’05]
Mobile participants are assumed to be connected from initializing the transaction until finishing the execution of their fragments
Transaction Commit On Timeout (TCOT) [TOC’02]
Uses timeouts to reduce the number of messages exchanged
Provides only semantic atomicity and not strict atomicity
Supports only one mobile participant
Entail high resource blocking time
Handle (small) subset of failures

6. Fault-Tolerant Pre-Phase Transaction Commit (FT-PPTC)
Main idea:
►Decouple commit of mobile participants from fixed participants
►Initial mobile commit, delegate problem to fixed part of network;
 Reduction of resource blocking time on fixed participants
 Re-use established protocols (commit, recovery, fault-tolerance)
CO distributes fragments first for mobile participants and waits for their execution results (Pre-Phase)
CO waits for a mobile participant for the timeouts that the participant initializes and updates (execution and shipping timeouts)
 CO waits for the slowest mobile participant and proceeds with the following phase iff the pre-phase succeeds
Handles network and node heterogeneity
Each mobile participant is represented in the fixed network by a proxy called mobile host agent (MH-Agent)
 Handles failures: Crash, disconnection, wireless message loss …

7. Send corresponding execution fragment
The FT-PPTC Protocol
Initiator
Coordinator
MH-Agent
Mobile Participant
Fixed Participant
Begin
Send transaction
& own timeouts
Forward fragment
Send corresponding execution fragment
Send timeouts
Forward timeouts
Hetero-
geneity ~
Pre-Commit Phase ~
Send updates
Send YES Vote
Send updates
Fixed Participant
Execution fragment
Ack
2PC
Prepare
Core 2PC Phase
Vote
Decision
Decision
Decision
Ack
Ack
Ack
End
Release
resources
Release
resources
Release
resources

8. FT-PPTC: Failure Resilience Scenarios
Initiator
Coordinator
MH-Agent
Mobile Participant
Begin
Send transaction
and timeouts
Forward fragment
Send corresponding execution fragment
Send timeouts
Transient
Disconnect.
Forward timeouts ~
Pre-Commit Phase ~
Extend timeouts
Forward extended timeouts
Send updates ~
Permanent
failures
Send updates
Send YES Vote
Fixed Participant
Execution fragment
Ack
2PC
Prepare
Core 2PC Phase
Vote
Decision
Decision
Decision
Ack
Ack
Ack
End
Release
resources
Release
resources
Release
resources

9. Implementation J2ME: Apache Derby = IBM Cloudscape Database
Personal Profile
IBM J9 Java Virtual Machine
Apache Derby = IBM Cloudscape Database
Mobile Device: PDA with Windows Mobile

10. “fastest” {link + participant} “slowest” {link + participant}
Timeout Selection
Higher #Transactions
Timeout selection
lower than
“fastest” {link + participant}
Optimal
timeout
selection
Timeout selection
higher than
“slowest” {link + participant}

11. Transaction Throughput
Tolerable decrease
Reasons for throughput decrease:
Communication bottlenecks
Processing/storage resources bottlenecks (Transaction blocking time on most involved resources is a key metric)

12. Blocking Time
Transaction blocking time on servers is constant (independent from the number of started transactions)

13. Conclusions and Future Work
Fault-tolerant & delay-aware atomic commit protocol for mobile transactions
Decouples commit of mobile participants from fixed participants
 Minimizes blocking time of resources on fixed part of the network
 Provides resilience to both communication and node failures
Future work
Consider ad-hoc communication between the mobile devices

14. Questions ?
Brahim Ayari, Abdelmajid Khelil, Neeraj Suri and Eugen Bleim
Department of Computer Science
TU Darmstadt, Germany
{brahim, khelil,