Mishra, S., Peterson, L. L. and Schlichting, R. (1993) Experience with modularity in Consul. Software Practice & Experience, 23, 1059--1075.  Home/Search   Document Details and Download   Summary   Related Articles   Check

.... on reliable multicast are surveyed in the next two sections, such as Isis and Horus systems of Birman [1, 2] token list [3] and its implementation [4] sequencer [5, 6] two phase [7, 8] tree [9] logical token ring [1, 10, 11] 3 phase [12] discrete acknowledgments [13, 14] and module [2, 15, 16] etc. We classify the well known algorithms as token passing, discrete acknowledgement and two phase approaches and briefly describe their features and associated problems. 1.1. Token passing approach Among the existing multicast techniques, the token passing approach is relatively simple ....

Mishra, S., Peterson, L. L. and Schlichting, R. (1993) Experience with modularity in Consul. Software Practice & Experience, 23, 1059--1075.

....services efficiently. 2 Related Work There is a great deal of research in the area of fault tolerant distributed systems, both in theory and in practice. In many high availability systems, the service layers of multicast communication and membership maintenance are intertwined together (e.g. [46, 47, 16, 13, 33, 24]) Therefore, in this section, we relate our work to several types of efforts: 1. Multicast communication protocols. 2. Membership algorithms. 3. General high availability projects. Multicast Communication Protocols The V system [21] was the first to introduce the concept of process group ....

....The second track provides real time services for semi active replication, within an extra performance architecture. In the extra performance architecture, special homogenous machines are utilized, as well as special purpose network hardware. The Consul project of the University of Arizona [47, 46] supports object replication. The system is implemented in a mudular object oriented approach, on top of the X kernel. It employs the Psync communication substrate for multicast communication, and thus allows the user to define semantically dependent multicast orderings. The system supports ....

S. Mishra, L. L. Peterson, and R. L. Schlichting. Experience with Modularity in Consul. Software Practice and Experience, 23(10):1059--1076, October 1993.

....to increase performance by partitioning the computational load, or to support rapid dissemination of information from senders to a group of potentially anonymous recipients. Numerous group communication systems have been developed during the last decade. Totem [1] ISIS [2] Horus [3] Consul [4, 5], Delta 4 [6] Amoeba [7] and Transis [8] are examples of such systems. These systems allow a set of processes to communicate using various delivery semantics such as FIFO, causal, or total ordering while providing a consistent membership view of participants believed to be accessible. A number ....

S. Mishra, L. Peterson, and R. Schlichting, "Experience with modularity in Consul," Software-- Practice and Experience, vol. 23, no. 10, pp. 1059--1075, October 1993.

....libraries of communication protocols. The Streams framework [25] a pioneer in the domain, and the x Kernel [23] contain rich libraries of communication protocols, but they do not deal with reliability and agreement issues. More recently, both in the context of the Horus [28] and the Consul [20] projects, libraries or reliable distributed protocols were provided. The proposed approaches consider however the group abstraction as the basic abstraction for reliable programming, and hence limit the scope of both environments. As we have discussed in section 1, transaction oriented ....

....order problem. There are many research works on how to design distributed environments in terms of objects, but protocols are usually not modeled as classes. Streams [25] and x Kernel [23] provide libraries of communication protocols but do not address fault tolerance, while Horus [28] and Consul [20] do. However, none of those systems view protocols as classes: protocols are dealt with as sets of functions. Bast is the only library of protocol classes we know of that addresses reliability issues. Furthermore, it provides protocol classes that support both the transaction paradigm and the ....

S. Mishra, L. Peterson, and R. Schlichting. Experience with modularity in Consul. Software-Practice and Experience, 23(10):1053--1075, October 1993.

....of group communication protocols. The Streams framework [31] a pioneer in the domain, and the x Kernel [29] contain rich libraries of communication protocols, but they do not deal with reliability and agreement issues. More recently, both in the context of the Horus [35] and the Consul [25] projects, libraries or reliable distributed protocols were provided. The proposed approaches consider however the group abstraction as the basic abstraction for reliable programming, and hence limit the scope of both environments. Transactionoriented applications are very difficult to support on ....

S. Mishra, L. Peterson, and R. Schlichting. Experience with modularity in Consul. Software Practice and Experience, 23(10):1053-- 1075, October 1993.

....all processes to execute join and leave operations. It detects processes that are no longer functioning and removes them from the group after agreement is reached with the other correctly functioning members. Consul has been successfully implemented as a modular system using the x kernel [MPS93b, MPS93c] However, as mentioned in Chapter 1, this implementation effort revealed that more support for modularity was needed for complex protocols that can be subdivided into many communicating submodules. 2.1.3 ISIS The ISIS distributed programming toolkit has been used to develop many ....

....has worked well for a large class of protocols, a persuasive case can be made that it lacks the flexibility needed to implement certain types of protocols. For example, in designing and implementing Consul using the x kernel, a number of inherent problems with the model were discovered [MPS93b] These problems can be summarized briefly as follows: ffl Provisions for communicating between protocol objects on the same machine are insufficient to implement the necessary complex interactions. In the x kernel, the specific problem is that the Uniform Protocol Interface (UPI) lacks ....

S. Mishra, L. L. Peterson, and R. D. Schlichting. Experience with modularity in Consul. Software--Practice & Experience, 23(10):1059--1075, October 1993.

....the same time, these messages will be delivered in the same order on all nodes. Therefore, the corresponding state changes occur in the same order. Other multicast or broadcast services provide different sets of properties. The Vsystem [CZ85] provides only unreliable multicast. Consul [MPS93a, MPS93b] Isis [BSS91] and Transis [ADKM92b, DM96] provide multicast with the atomicity property and various ordering properties, but no timeliness properties. The Mars system [KO87, KDK 89] provides atomicity, ordering, and timeliness properties. The existing multicast implementations cover only a ....

....fault tolerant distributed computing, only a few have explored modularity and configurability. The most notable of these are the Consul and Horus systems. Consul is a collection of protocols developed for implementing fault tolerant distributed programs based on the state machine approach [MPS93a, MPS93b] It provides support for ordered multicast, membership, and recovery, where the different services are implemented as modules using the x kernel. Although configurable, the different choices available for the application builder are limited to different message ordering properties. The Horus ....

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S. Mishra, L. Peterson, and R. D. Schlichting. Experience with modularity in Consul. Software Practice & Experience, 23(10):1059--1075, Oct 1993.

....Bast can be used. Modeling communications Several systems try to model communications but do not address reliability issues, e.g. Streams [14] and the x Kernel [13] Other systems offer reliable distributed communications, either based on groups as elemental addressing facilities, e.g. Consul [12], Isis [1] and Horus [18] or based on transactions, e.g. Arjuna [17] Most of these systems merely provide a non extensible library of communication protocols. With Bast, we have tried to model any kind of interaction between distributed object, not only communications. This is necessary if we ....

S. Mishra, L. Peterson, and R. Schlichting. Experience with modularity in Consul. Software-Practice and Experience, 23(10):1053--1075, October 1993.

....complex protocols are concerned. Besides, those abstractions are very primitive when it comes to deal with reliability issues, i.e. when one wants to seamlessly cope with failures. Many systems do provide facilities to achieve reliability (Birman and Renesse, 1993; van Renesse and Birman, 1995; Mishra et al. 1993; Shrivastava et al. 1991) but they are closely bound to either the group model or to the transaction model. 1.2 Why Model Protocols as Objects Building distributed systems is challenging, because many complex problems have to be dealt with, e.g. remote communications, failures detections, ....

....define several abstractions, whereas our approach is based on only two concepts: protocols as objects and their composition through protocol algorithm objects. 4. 2 Representing Communication Protocols Systems like ISIS (Birman and Renesse, 1993) HORUS (van Renesse and Birman, 1995) and CONSUL (Mishra et al. 1993) all provide reliable distributed protocols, but groups are the elemental distributed addressing facilities. The ARJUNAsystem (Shrivastava et al. 1991) allows to deal with failures by providing communications based on transactions. Because these approaches strongly couples reliability issues ....

Mishra, S., Peterson, L., and Schlichting, R. (1993). Experience with modularity in Consul. Software Practice and Experience, 23(10):1053--1075.

....[17] AVOCA [24] defines the notion of protocol objects, but not in the sense that BAST does; furthermore, it mainly applies to highperformance communication subsystems. Other systems offer reliable distributed communications, either based on groups as elemental addressing facilities, e.g. CONSUL [15], ISIS [1] and HORUS [23] or based on transactions, e.g. ARJUNA [22] Microprotocols and the x Kernel The work done by O Malley and Peterson [16] is the closest to BAST that we could find. They extended the x Kernel with the notion of microprotocol graph, and they described a methodology for ....

S. Mishra, L. Peterson, and R. Schlichting. Experience with modularity in Consul. Software Practice and Experience, 23(10):1053--1075,October 1993.

....to facilitate configurability without adversely affecting programmability. All this derives from our experience with the Consul system, which suggests that current techniques are inadequate for supporting modularity in the type of complex protocols often found in fault tolerant distributed systems [16]. Other researchers have also proposed modular implementations of RPC. For example, in [13] a modularization technique also based on the x kernel is described. In contrast with our emphasis on modularizing along the lines of abstract properties, however, that paper describes a more syntactic ....

S. Mishra, L. L. Peterson, and R. D. Schlichting. Experience with modularity in Consul. Software Practice & Experience, 23(10):1059--1075, Oct 1993.

....token passing, are used by the membership service itself to communicate with peers on other sites. 3.4 Shared data structures One of the most important benefits of using composite protocols is that it allows micro protocols to share data. Our experience using the x kernel to construct Consul [MPS93b] suggests that shared data facilitates implementation of modular fault tolerant services, as does the experience reported independently by the developers of the xAMP atomic multicast suite [Fon94] In the configurable membership service, the most important shared data structures are the ....

S. Mishra, L. L. Peterson, and R. D. Schlichting. Experience with modularity in Consul. Software Practice & Experience, 23(10):1059--1075, Oct 1993.

....facilitate configurability without adversely affecting programmability. All this derives from our experience with the Consul system, which suggests that current techniques are inadequate for supporting modularity in the type of complex protocols often found in fault tolerant distributed systems [MPS93] Other researchers have also proposed modular implementations of RPC. For example, in [HPOA89] a modularization technique also based on the x kernel is described. In contrast with our emphasis on modularizing along the lines of abstract properties, however, that paper describes a more ....

S. Mishra, L. L. Peterson, and R. D. Schlichting. Experience with modularity in Consul. Software Practice & Experience, 23(10):1059--1075, Oct 1993.

.... atomic multicast [MPS93a, PBS89] highlighted deficiencies in several areas, including support for complex interactions among protocol objects, limited facilities for data sharing, and an orientation towards hierarchical protocol composition at the expense of more flexible combinations [MPS93b] The developers of xAMP, a real time atomic multicast protocol, report a similar experience [Fon94, VRB89] The lack of a sufficiently rich protocol object interface has also been cited as one of the motivations for developing Horus [RBM96] In addition, our approach is related to recent work in ....

....and can interact in arbitrary ways. As already noted, the inclusion of facilities for non hierarchical composition was prompted in large part by limitations in a purely hierarchical model encountered when using hierarchical systems to construct group communication protocols [Fon94, MPS93b] With Coyote, designers have the ability to use both hierarchical and non hierarchical composition within the same system as needed. The computational model supported by Coyote also results in differences with the Horus and Ensemble approach. For example, events in Coyote are a general mechanism ....

S. Mishra, L. Peterson, and R. Schlichting. Experience with modularity in Consul. Software: Practice and Experience, 23(10):1059--1075, Oct 1993.

....approach has worked well for a large class of protocols, a persuasive case can be made that it lacks the flexibility needed to implement certain types of protocols. For example, in designing and implementing Consul using the x kernel, a number of inherent problems with the model were discovered [30]. These include the following: ffl Provisions for communicating between protocol objects on the same machine are insufficient to implement the necessary complex interactions. In the x kernel, the specific problem is that the UPI lacks sufficient flexibility, thus requiring the programmer to use ....

....and data sharing, while retaining the programming and configurability advantages of the x kernel. As noted above, the need for such facilities has been directly motivated by earlier experience using the x kernel to construct the type of high level protocols that are the target of this research [30]. Many of our goals related to system customization, code reuse, and protocol configurability are adopted from the x kernel. Other x kernel related work has explored the use of finergrain protocol objects [33] but the emphasis there is on syntactic decomposition of higher level protocols within ....

S. Mishra, L. L. Peterson, and R. D. Schlichting. Experience with modularity in Consul. Software Practice & Experience, 23(10):1059--1075, Oct 1993.

....programs can be built, provides support to manage communication, redundancy, failures, and recovery in a distributed system. Moreover, Consul is highly modular. Such modularization simplifies the development of new protocols, as well as increases the configurability of the resulting system [23]. The Psync protocol, a group oriented atomic multicast protocol that explicitly preserves the partial (or causal) order of messages, is at the heart of Consul [26] One of the novel aspects of Consul is that the other building block protocols take advantage of the partial ordering of messages ....

S. Mishra, L. L. Peterson, and R. D. Schlichting. Experience with modularity in Consul. Software Practice & Experience, 23, 1993. To appear.

....triggers an alarm if it suspects that another machine has failed, and Membership, which implements the agreement algorithm used to decide if a failure has indeed occurred. Recovery implements replica recovery using a combination of checkpoint and message replay. As described more fully elsewhere [MPS92a, MPS93] part of the reason for building Consul was to test whether it was possible to build a fault tolerant system of this type in a modular manner using traditional network protocol composition techniques. In general, we feel that this effort was successful; as can be seen from the figure, ....

S. Mishra, L. L. Peterson, and R. D. Schlichting. Experience with modularity in Consul. Technical Report 92-25, Dept of Computer Science, University of Arizona, Tucson, AZ, 1992.

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S. Mishra, L. L. Peterson, and R. Schlichting, `Experience with Modularity in Consul', Software-- Practice and Experience, 23(10), 1059--1075 (October 1993).

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Mishra, S., Peterson, L. L., and Schlichting, R. D. Experience with Modularity in Consul. Technical Report, Department of Computer Science, The University of Arizona, 1993.

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Shivakan Mishra, Larry L. Peterson and Richard D. Schlichting. Experience with Modularity in Consul. SoftwarePractice and Experience, 23:10 (Oct 1993), 10501075.

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