O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanisms. In S. J. Mullender, editor, Distributed Systems, pages 55--96. Addison-Wesley, 1993.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....this thesis will only discuss time driven discrete simulation models. A distributed system is a collection of sequential processes P 1 , P 2 , and P n , and a network of unidirectional communication channels. Each channel connects a pair of processes and delivers messages between them [3]. Distributed simulations typically provide more overall host processing power and more storage space than sequential simulation systems, and thus support more simulation entities and more detailed appearance and behaviors of entities within the system. The distributed structure also allows ....

....then e f if and only if [34] 1. a process executes both e and f , e occurs before f ; or 2. e = send(m) and f = receive(m) for some message m; or 3. there exists an event h, such that e h and h f . Then the causal ordering of events is defined as satisfying the following requirement [3]: send i (m) send j (m ) deliver k (m) deliver k (m ) for all messages m, m , sending processes p i , p j and destination process p k . 55 A widely used example to prove the necessity of maintaining causal order in a distributed system is shown in Figure 4.6. Since deliver 2 (m ....

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Ozalp Babaoglu and Keith Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanisms. In Sape Mullender, editor, Distributed Systems. ACM Press, 1993.

....established process migration model, and how these abstractions can be applied in our problem domain. 2.2 Distributed systems and distributed applications We will first determine how a distributed system can be defined. In the literature, a variety of explanations exist. Babaoglu and Marzullo [3] defines a distributed system as consisting of a collection of processes and a network capable of implementing communication channels between these processes. Identifying these two major components is important both during the system design phase, and when evaluating the final product. The ....

....is necessary. In his classic paper [33] Lamport shows how logical clock values can be used to synchronize the events of a system. The suggestion is to apply the events taken by the message exchange. These events may be used for synchronizing the sequential processes. Babaoglu and Marzullo [3] employs a general abstraction of FIFO delivery to show that the ordering of the messages can be maintained for all causally related messages, even if they are sent by independent processes. The resulting property is called causal delivery (CD) and may be expressed as: CD: send m send m deliver ....

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Babaoglu, Ozalp and Marzullo, Keith: "Consistent global states of distributed systems: Fundamental concepts and mechanisms", in "Distributed systems, 2. ed.", Mullender (ed.), ACM Press, 1993.

....may be found in [15] Aside from practical implementation work, much research has been devoted to the study of problems arising in distributed debugging. As noted before, we classify these problems into those that deal with observation and those that deal with control. Predicate Detection [1, 6] is the main problem involved in observing distributed computations. It involves detecting whether a specified global property ever occurs in a distributed computation. For example, one might wish to check that the validity of mutually exclusive sections of code is maintained. Predicate detection ....

O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: fundamental concepts and mechanisms. In S. Mullender, editor, Distributed Systems, chapter 4. Addison-Wesley, 1993.

....have to be computed. If the property is stable (once true it remains true forever) a snapshot algorithm can be used to detect it [3] When the property is not stable, all the global states, through which the computation could have passed, have to be considered. These states constitute a lattice [1, 15]; a node of the lattice represents a possible global state of the distributed computation and an edge represents an event that changes the global state of the computation. A general method to detect such unstable properties consists in building the lattice associated with the distributed execution ....

....[2, 12] this can be done on the fly by pipelining the construction and the traversal of the lattice with the execution. The basic problem with the detection of general (unstable) properties on global states is that the size of the lattice can be exponential with respect to the number of processes [1, 15]. However for some specific properties on global states such as conjunction of local predicates [9] relational global predicate [16] or inevitable global states [7, 9] the lattice construction is not necessary. The subject of this paper is the second class of properties, namely the ones on ....

O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: fundamental concepts and mechanisms, in Distributed Systems, chapter 4, pages 55--93. ACM Press, Frontier Series, (S.J. Mullender Ed.), 1993.

....algorithms that run on the system with mobile computing devices therefore require some modi cations to compensate for these factors. In this paper, we consider causal message ordering required in many distributed applications such as management of replicated data [8, 9] distributed monitoring [6], resource allocation [18] distributed shared memory [3] multimedia systems [2] and collaborative work [19] The protocols to implement causal message ordering in systems with static hosts have been presented in [14, 9, 16, 18, 20, 21] These protocols can be executed by every mobile host with ....

O. Babaoglu and K. Marzullo. Consistent Global States of Distributed Systems: Fundamental Concepts and Mechanisms. In Sape Mullender, editor, Distributed Systems, pages 55-96. Addison-Wesley, 1993.

....objects or actors which are garbage based on that graph. Since there is no omniscient observer in a distributed system, a global snapshot is usually constructed by taking a consistent cut of the global state and accounting for any messages in transit in the network. The reader is referred to [5, 34] for details. However, such a global snapshot approach requires synchronization among all the hosts in the system which raises questions about scalability. For this reason, most algorithms try to avoid taking a global snapshot. 35 There are several other algorithms available in the literature ....

Ozalp Babaoglu and Keith Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanisms. In S. Mullender, editor, Distributed Systems, pages 55--96. Addison-Wesley, 1993.

....perform the protocol. synchronous rounds: minimum number of synchronous rounds required by the protocol, presuming that every party is allowed to send arbitrarily many messages with every time tick and to receive arbitrarily many messages sent by other parties at the beginning of a round (cf. [BM93] p. 133) simple rounds: minimum number of required synchronous rounds, presuming that every party sends and receives at most one message per round (cf. ABM87] Whereas the total number of messages of a protocol measures the number of packages sent, the number of exchanges can be considered ....

Babaoglu, O., Marzullo, K., Consistent Global State of Distributed Systems: Fundamental Concepts and Mechanisms. In S. Mullender (ed.), Distributed Systems. NY: ACM Press, 1993, 55--145.

....perform the protocol. synchronous rounds: minimum number of synchronous rounds required by the protocol, presuming that every party is allowed to send arbitrarily many messages with every time tick and to receive arbitrarily many messages sent by other parties at the beginning of a round (cf. [BM93] p. 133) simple rounds: minimum number of required synchronous rounds, presuming that every party sends and receives at most one message per round (cf. ABM87] Whereas the total number of messages of a protocol measures the number of packages sent, the number of exchanges can be considered ....

Babaoglu, O., Marzullo, K., Consistent Global State of Distributed Systems: Fundamental Concepts and Mechanisms. In S. Mullender (ed.), Distributed Systems. NY: ACM Press, 1993, 55--145.

....of dependent events and observation [5] In many applications, causal order based on logical time is not enough to capture the dependencies needed by the application s logic. Vector clocks bring progress over logical (scalar) timestamps by inducing an order that exactly reflects causal precedence [6 8]. Matrix clocks [9, t0] extend vector clocks by cap turing a global property, namely what A knows about what B knows about C . Such shared knowledge is needed in many instances involving close cooperation, such as replica update management and collaborative work. However, matrix clocks require ....

O. Babaoglu and K. Marzullo. Consistent Global States of Distributed Systems: Fundamental Consepts and Mechanisms, chapter 3. S. Mullenderr, addison-wesley edition, 1993.

....entities that have significant nonlinear movements and action vocabularies. A distributed system is a collection of sequential processes P 1 , P 2 , and P n , and a network of unidirectional communication channels. Each channel connects a pair of processes and delivers messages between them [2]. Distributed simulations typically provide more overall host processing power and more storage space than sequential simulation systems, and thus support more simulation entities and more detailed appearance and behaviors of entities within the system. The distributed structure also allows ....

Ozalp Babaoglu and Keith Marzullo: "Consistent Global States of Distributed Systems: Fundamental Concepts and Mechanisms" In Sape Mullender, editor, Distributed Systems. ACM Press, 1993.

....is changed for a move out event, a message is sent which notifies the next cell of the change. In our implementation, the GVT (global virtual time) computation is performed by means of a coloring algorithm [22] to determine the set of all the messages in transit before a certain consistent cut [2] of the distributed computation. A token message circulates among all processes in Stage 2, along a predefined and fixed virtual ring of processes. The computation of each process is cyclically colored with one of three colors (white, black, and red) and the current color is given to all messages ....

O. Babaoglu and K. Marzullo, Consistent global states of distributed systems: fundamental concepts and mechanisms, in: Distributed Systems (Addison-Wesley, 1995)

....to visualize concurrent execution, the statetransition approach requires a global snapshot of algorithm state. Unfortunately, in distributed environments global snapshots are costly due to distributed state and asynchrony, and may not correspond to any state entered by the underlying execution [23]. Moreover, semantically equivalent execution behavior may yield different state transitions. As a result, the statetransition approach is costly to implement and does not effectively abstract over the relevant behavior in distributed systems. A more natural model for visualizing distributed ....

....on visualization actions: Causal Connection Restriction: The invocation order of visualization actions must preserve the causal order of actor events which trigger them. Note that under the casual connection restriction, the resulting visualization always corresponds to a consistent cut [23] of the triggering events in the underlying execution. A B C A 1 B 1 B 2 C 1 C 2 Figure 2.2: Event Diagram. Three actors A, B and C are shown together with their visualization events. Figure 2.2 illustrates how the causal connection restriction affects visualization. The event ....

[Article contains additional citation context not shown here]

Ozalp Babaoglu and K. Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanisms. In S. Mullender, editor, Distributed Systems, chapter 4, pages 55--96. ACM Press, New York, NY, 1994.

....have been moved to CLP1. 5 Open Issues A number of challenging issues have to be addressed before this approach is realised. Techniques are required to obtain global snapshots of the distributed simulation and approximate the spheres of influence at any instant, e.g. Chandy Lamport 1985, Babaoglou Marzullo 1993). Furthermore, algorithms for redistributing the state and reorganising the tree to approximate the spheres of influence and balance the load to achieve high simulation performance must be developed; in this context appropriate performance metrics and cost functions need to be defined which will ....

Babaoglou, O. & Marzullo, K. (1993), Consistent global states of distributed systems: Fundamental concepts and mechanisms, Technical Report UBLCS-93-1, Laboratory for Computer Science, University of Bologna.

....algorithms that run on the system with mobile computing devices therefore require some modifications to compensate for these factors. In this paper, we consider causal message ordering required in many distributed applications such as management of replicated data [8, 9] distributed monitoring [6], resource allocation [18] distributed shared memory [3] multimedia systems [2] and collaborative work [19] The protocols to implement causal message ordering in systems with static hosts have been presented in [14, 9, 16, 18, 20, 21] These protocols can be executed by every mobile host with ....

O. Babaoglu and K. Marzullo. Consistent Global States of Distributed Systems: Fundamental Concepts and Mechanisms. In Sape Mullender, editor, Distributed Systems, pages 55--96. Addison-Wesley, 1993.

....algorithms that run on the system with mobile computing devices therefore require some modifications to compensate for these factors. In this paper, we consider causal message ordering required in many distributed applications such as management of replicated data [5, 6] distributed monitoring [4], resource allocation [11] distributed shared memory [2] multimedia systems [1] and collaborative work [12] The protocols to implement causal message ordering in systems with static hosts have been presented in [7, 6, 9, 11, 13, 14] These protocols can be executed by every mobile host with ....

O. Babaoglu and K. Marzullo. Consistent Global States of Distributed Systems: Fundamental Concepts and Mechanisms. In Sape Mullender, editor, Distributed Systems, pages 55--96. Addison-Wesley, 1993.

....and part of the state is feasible. However, a number of challenging issues have to be addressed before this approach is realised. Techniques are required to obtain global snapshots of the distributed simulation and approximate the spheres of influence at any instant, e.g. Chandy Lamport 1985, Babaoglou Marzullo 1993) Furthermore, algorithms for redistributing the state and reorganising the tree to approximate the spheres of influence and balance the load to achieve high simulation performance must be developed; in this context appropriate performance metrics and cost functions need to be defined which will ....

Babaoglou, O. & Marzullo, K. (1993), Consistent global states of distributed systems: Fundamental concepts and mechanisms, Technical Report UBLCS-93-1, Laboratory for Computer Science, University of Bologna.

....for every state S i in the observation the next state S i 1 is the result of a single event on one process. In this case we say that S i precedes S i 1 . It can be shown that the set of all consistent global states together with the transitive closure of the precedes relation forms a lattice [1, 13]. Every consistent observation corresponds to a path through the lattice starting at the top element, so observations are not observer independent [13] Given some predicate and by using this lattice, it is possible to define two observer independent notions of observation in the following way ....

....up arrays at different monitors by a superscript, i.e. up j refers to the array on monitor b j . The correspondence is as follows: Process p i has crashed iff up[i] false. Assuming n = 3, the predicate stating that exactly two processes have crashed can be formalized as ( up[1] :up[2] up[3] up[1] up[2] up[3] up[1] up[2] up[3] A question related to this way of formalization is the following: Consider a process p i which has a local variable x initially set to 1. The predicate which we want to detect is x 6= 1. As long as p i is up and ....

[Article contains additional citation context not shown here]

O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanisms. In S. Mullender, editor, Distributed Systems, chapter 4, pages 55--96. Addison-Wesley, second edition, 1993.

....a computation: Although script driven probing and fault injection has been applied to several complex communication protocols and distributed applications, we need to develop a formal framework for orchestrating a computation. Past work on global snapshots or global 20 predicate detection [4] is closely related to this problem. Furthermore, we need to identify a minimal set of primitives for injecting faults given a certain failure model. Acknowledgment This work is supported by a grant from the U.S. Office of Naval Research. We are very grateful to Jerry Toporek at Mentat for ....

O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanism. In Sape Mullender, editor, Distributed Systems. Addison Wesley, 1993. Second Edition.

....system (a snapshot) at any particular moment. In sequential programming this is straightforward. In distributed simulations however snapshots are not easily obtainable; to determine the system state, all the different local process as well as channel states need to be taken into account [Chan85] [Baba93]. The monitoring system should be able to correlate the histories of the different processes and put them in a global temporal perspective. This is a complicated issue related to the problem of dealing with causality in a distributed environment, discussed in section 3.4. An approach for ....

Babaoglou, O., Marzullo, K., "Consistent Global States of Distributed Systems: Fundamental Concepts and Mechanisms", Technical Report UBLCS-93-1, Laboratory for Computer Science, University of Bologna, January 1993.

No context found.

O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanisms. In Sape Mullender, editor, Distributed Systems, pages 55--96. Addison-Wesley, 1993.

....As an alternative to proving properties a priori, they can be checked concurrently with an actual execution of the program through run time property detection. With this technique, conclusions that are drawn are not about all possible executions of the program, but about all possible observations [SM94, BM93] of an actual execution. The third alternative reasoning about program properties after an execution is called post mortem analysis and is similar to run time property detection. The basic difference is that the analysis has to be based on data collected during the execution (traces) and ....

....i is the global state that results after executing event e i in Sigma i Gamma1 . By construction, each path of the lattice starting at the minimal element and proceeding upwards corresponds to an observation of the computation and each observation corresponds to a path in the lattice [BM93, SM94]. In other words, the lattice of consistent global states represents all possible observations for the computation. Note that, internal to the computation, the actual sequence of global states that is produced cannot be known and this lattice represents the best information that is available. PI ....

O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: fundamental concepts and mechanisms, in Distributed Systems, chapter 4, pages 55-- 93. ACM Press, Frontier Series, (S.J. Mullender Ed.), 1993.

No context found.

O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanisms. In S. J. Mullender, editor, Distributed Systems, pages 55--96. Addison-Wesley, 1993.

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 O. Babaoglu and K. Marzullo. Consistent Global States of Distributed Systems: Fundamental Concepts and Mechanisms, chapter 4, pages 55-96. In: S. Mullender (Ed.) - Distributed Systems, Addison-Wesley, 1993.

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O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: Fundamental concepts and mechanisms. In S. J. Mullender, editor, Distributed Systems, pages 55--96. Addison-Wesley, 1993.

No context found.

O. Babaoglu and K. Marzullo. Consistent global states of distributed systems: fundamental concepts and mechanisms. In S. Mullender, editor, Distributed Systems, chapter 4. Addison-Wesley, 1993.

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