Monitoring distributed systems using knowledge

Question

1. What are the contributions mentioned in the paper "Monitoring distributed systems using knowledge" ?

2. What is the definition of a Petri net?

3. What is the second iteration of the Petri net?

4. How do the authors achieve a synchronization of a distributed system?

Accepted Answer

In this paper, the authors use knowledge-based control theory to monitor global properties in a distributed system.. The authors control the system to enforce that if a given global property is violated, at least one process knows this fact, and therefore may report it.. Their approach uses knowledge properties that are precalculated based on model checking.. Since synchronizations are expensive, the authors aim at minimizing their number using the knowledge analysis.

Accepted Answer

Petri net can be seen as a distributed system, consisting of a set of concurrently executing and temporarily synchronizing processes.

Accepted Answer

The second iteration terminates as soon as ∆ becomes an invariant or if all knowledgeable steps for pairs of processes not strictly including knowledgeable steps consisting of single processes have been added to the table.

Accepted Answer

To realize at runtime the temporary synchronizations needed to achieve such combined knowledge, asprecalculated using the knowledge analysis at compile time, a synchronization algorithm (such as α-core [14]) is used.

Accepted Answer

Their approach for achieving a local or semi-local decision on which transitions may be fired, while preserving observability, is based on the knowledge of processes [5] or sets of processes.

Accepted Answer

If ∆ is an invariant after the first iteration, then taking only knowledgeable steps appearing in ∆ does not introduce deadlocks.

Accepted Answer

The correctness of the algorithm guarantees the atomic-like behavior of the coordination process, allowing us to reason at a higher level of abstraction where the authors treat the synchronizations provided by α-core (or any similar algorithm) as transitions that are joint between several participating processes.

Accepted Answer

If the authors consider 6 trains, there are 820,368 reachable global states in this example, of which 11,830 contain a partial gridlock and 48 are global deadlock states.

Accepted Answer

the number of synchronizations due to the monitoring policy is very low and although the only progress property that the authors preserve is deadlockfreedom, few transitions are inhibited in this example.

Accepted Answer

An extended Petri net N ′ consists of (1) a Petri net N (2) a finite set of variables V with given initial values and (3) for each transition t ∈ T , an enabling condition ent and a transformation predicate ft on variables in V .

Accepted Answer

If ∆ is still not an invariant, then the authors perform further iterations where the authors consider knowledgeable steps for triples of processes, and so forth.

Accepted Answer

The authors first calculate in which local states a process has enough information to identify that ψ is violated: in each reachable global state in which ψ becomes false, at least one process must detect this situation.

Monitoring distributed systems using knowledge

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Most frequently asked questions

1. What are the contributions mentioned in the paper "Monitoring distributed systems using knowledge" ?

2. What is the definition of a Petri net?

3. What is the second iteration of the Petri net?

4. How do the authors achieve a synchronization of a distributed system?

5. What is the approach for achieving a local or semi-local decision on which transitions?

6. What does it mean to take only knowledgeable steps?

7. What is the correctness of the algorithm?

8. How many reachable global states are there in this example?

9. How many transitions are inhibited by the monitoring policy?

10. What is the definition of an extended Petri net?

11. What is the way to determine if is an invariant?

12. How do the authors calculate the state of a process?

Figures

Citations

Efficient and Generalized Decentralized Monitoring of Regular Languages

New Results - Organising LTL monitors over distributed systems with a global clock

Efficient and Generalized Decentralized Monitoring of Regular Languages

Assumption-Based Runtime Verification with Partial Observability and Resets

Organising LTL Monitors over Distributed Systems with a Global Clock

References

Reasoning About Knowledge

Distributed snapshots: determining global states of distributed systems

Formal verification of parallel programs

On the synthesis of strategies in infinite games

Contentment in graph theory: Covering graphs with cliques

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