1. Version-consistent Dynamic Reconfiguration of Component-based Distributed Systems Authors: Xiaoxing May, Luciano Baresi, Carlo Ghezzi, et. al. ABSTRACT 1. There is an increasing demand for the runtime reconfiguration of distributed systems in response to changing environments … 2. Reconfiguration must be done in a safe and low-disruptive way. 3. In this paper, we propose version consistency of distributed transactions as a safe criterion for dynamic reconfiguration. 4. Version consistency ensures that distributed transactions be served as if there were operating on a single coherent version of the system despite possible reconfigurations that may be happening. 5. The paper also proposes a distributed algorithm to maintain dynamic dependences between components at architectural level and enable low-disruptive version-consistent dynamic reconfigurations. ESEC/FSE’11. 5-9 th September, 2011, Szeged, Hungary.

2. Aim It is necessary to modify existing parts of the implementation or add new functionality at runtime without blocking the system and preserving the correct completion of on- going activities.

3. Dynamic Update Example Idle – Not currently hosting transactions Quiescence – Not engaged in a transaction that it initiated – It will not initiate a new transaction – It is not currently engaged in servicing a transaction – No transactions have been, or will be initiated by other nodes which require this service

4. Dynamic Reconfiguration Quiescence-Based Approach Quiescence-Based Approach : i.Considers static dependencies between components. ii.Must be conservative due to reconfiguration being oblivious to system states. iii.Pessimistic view of transactional dependencies results in more disruption than the ideal.

5. Dynamic Reconfiguration Version Consistent Version Consistent Approach : i.Considers dynamic dependencies between components. ii.Extends dynamic dependencies to ensure ‘global’ consistency through the notion of version consistency iii.Introduces less disruption because component can be updated when not in a quiescent state.

6. Concept Version Consistent Approach : i.Considers dynamic dependencies between components. ii.Extends dynamic dependencies to ensure ‘global’ consistency through the notion of version consistency iii.Introduces less disruption because component can be updated when not in a quiescent state.

7. Model Definition

8. Version Consistent - Example

9. Performance

10. Applicability There are two views of Dynamic Reconfigurablity to consider 1.Reconfiguration using process 2.Reconfiguration using functionality (VC) VC assumes static process and does not appear to be feasible for shared processes My thesis is based on process layering with static functionality The melding of both methods and incorporating rule based updates may be worth considering in future work.

11. QUESTIONS Presented by Alexander Cameron