1. Group Service in CORBA Xing Gang Supervisor: Prof. Michael R. Lyu
Marker: Prof. Irwin K. C. King, Prof. John C. S. Lui
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2. Outline Motivation Background OmniORB Proposed System Schedule
Group Service
Group-based System
Group Communication in CORBA
CORBA FT Service
OmniORB
Proposed System
Schedule
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3. Motivation Goal Use Group Service to Manage the Redundant Entity
Provide Fault Tolerance via Entity Redundancy
Use Group Service to Manage the Redundant Entity
Group Service: Provide Reliable Group Communication (multicast)
CORBA FT Service Specification
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4. Idea of Group Communication
Group Communication is to gather a set of processes or objects into a logical group, and to provide primitives for sending messages to all group members at the same time with various ordering guarantees
A group constitutes a logical addressing facility since messages can be issued to groups without having to know
the number, identity, or location of individual members. Groups have proven to be very useful for providing high availability through replication: a set of replicas constitutes a group, viewed by clients as a single entity in the system.
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5. Total Order Multicast 5/3/2019
Total order multicast is one of the most useful primitives for group communication. Simply stated, it ensures that messages sent to a group are delivered in the same order to all members of the group. Total ordering of messages is required for instance
in replication, to ensure that the replicated data is kept consistent. Figure 1.2 shows two messages sent by two clients to a set of servers with and without total ordering. A total order protocol may need to delay the actual delivery of a message to the application for ensuring correct ordering.
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6. Active Replication
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7. Primary-Backup Replication
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8. Group-Base System Isis Horus Ensemble (Maestro): Cornell Univ.
Totem: UCSB
Transis: Hebrew Univ.
Phoenix: Swiss FIT
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9. Different Approaches
Integration Approach : integrates an existing group communication system within an ORB
Interception Approach : intercepts messages issued by an ORB and maps them to a group communication toolkit
Service Approach : provides group communication as a CORBA service beside the ORB
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10. Integration Approach
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11. Orbix+Isis
Orbix
Client
Isis
Server1
Server2
Server3
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12. Interception Approach
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13. Eternal
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14. Service Approach
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15. OGS
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16. Approaches Comparison
Integration
Interception
Service
Transparency +
Ease of Use
Portability
Interoperability
Modularity
CORBA Compliance
Performance
Simplicity
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17. CORBA FT Service(1) Time Line Objective Wide range of fault tolerance
RFP Issued -- April 1998
Initial Proposals Submitted -- October 1998
Joint Revised Submission -- October 1999
Approved by OMG – December 1999
Objective
Wide range of fault tolerance
Simple low-cost clients
Highly reliable servers
Passive and Active replication
Both automatic and application-controlled fault tolerance mechanisms
Strong replica consistency, when needed
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18. CORBA FT Service(2) Fault Tolerance Properties Replication Styles
Infrastructure-Controlled and Application-Controlled
Object Group References and Alternative Destinations
At-Most-Once Invocation
Fault Detection and Notification
Checkpointing and Logging
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19. Architectural Overview
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20. omniORB
omniORB is a robust, high-performance CORBA 2 ORB, developed by AT&T Labs research
omniORB is freely available under GPL
Feathers
C++ binding
Native IIOP
Multithread
Naming and Lifecycle Service
omniORB3
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21. Add Group Service to omniORB
Objective
Robustness
Completeness
Performance
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22. ORB Multicasting
Enhance POA to provide group management interface to ORB
Multicast Algorithms (protocol)
Isis/Hours/Ensemble
Totem
Transis
Semiotics
at least once
at most once
exactly once
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23. Assumptions No Low Level Group Communication Toolkit NO IP Multicast
No Network Partition Problem
Higher Level Group Management Service
Use CORBA FT Service Interface
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24. Active Replication Requirement Group Management (AT&T)
Multicast Implementation
Fault Tolerance Service Spec. Compliance
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25. Experimentation & Evaluation
Application
Active Replicate Name Server
Evaluation of Current Specification
Discovery
Overhead
Reliability
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26. Schedule Multicast Protocol
August 31,2000
Integrate with AT&T Group Management Service
November 30,2000
Applications & Evaluation
March 31,2000
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27. Q&A
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28. Thank You!!
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