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... servers’ clocks reasonably close is desirable so that the induced Write order is consistent with a user’s perception of the order in which Writes are submitted. Bayou servers maintain logical clo=-=cks [20] t-=-o timestamp new Writes. A server’s logical clock is generally synchronized with lts real-time system clock, but, to preserve the causal ordering of Write operations, the server may need to advance i...

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...clients and other servers, uses a simple decentralized registration and lookup service for key-value pairs that are made wsible across a network via multicast. Bayou merge procedures are Tcl programs =-=[24]-=- that are run in a Tcl interpreter modified to enforce the limits described in Section 5. We foresee that these components may change as the system evolves. The two running apphcations have demonstrat...

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...ess control and authentication in Bayou posed interesting challenges because of our minimal connectivity assumptions. In particular, the design cannot rely on an online, trusted authentication server =-=[23]-=- to mediate the establishment ofssecure channels between a client and server or between two Bayou servers. As an example, suppose two users holding Bayou rephcas on their portable computers are in a m...

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... consideration characteristics of mobile computing such as expensive connection time, frequent or occasional disconnections, and that collaborating computers may never be all connected simultaneously =-=[1, 13, 16]. Th-=-e Bayou architecture does not include the notion of a “disconnected” mode of operation because, in fact, various degrees of Mike J. Spreitzer and Carl H. Hauser Computer Science Laboratory Xerox P...

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...akly consntent replication model with a read-uny/write-any style of access. Weakly consistent replication has been used previously for availability, simplicity and scalability in a variety of systems =-=[3, 7, 10, 12, 15, 19]-=-.sAnti-entropy While individual Read and Write operations are performed at a single server, clients need not confine themselves to interacting with a single server. Indeed, in a mobile computing envir...

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...lar instance of the system: a server and client for the bibliographic database described in Section 2. The database is composed of a single table containing 1550 tuples, obtained from a bibtex source =-=[21]-=-. Each tuple was inserted into the database with a single Bayou Write operation. Results are presented for five different configurations of the database characterized by the number of Writes that are ...

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...cit coordination with other rephcas. Every computer eventually receives updates from every other, either directly or indirectly, through a chain of pair-wise interactions. Unhke many previous systems =-=[12, 27]-=-, our goal m designing the Bayou system was not to provide transparent rephcated data support for existing file system and database applications. We believe that applications must be aware that they m...

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...lude arbitrary merge procedures, it is effectively impossible either to determine whether two Writes commute or to transform two Writes so they can be reordered as has been suggested for some systems =-=[9]-=-. When a Write is accepted by a Bayou server from a client, it is initially deemed tentative. Tentative Writes are ordered according to timestamps assigned to them by their accepting servers. Eventual...

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...since these naturally depend on the semantics of the application. To this end, Bayou provides system support for applicatlonspecific confllct detection and resolution. Previous systems, such as Locus =-=[30]-=- and Coda [17], have proven the value of semantic conflict detection and resolution for file directories, and several systems are exploring conflict resolution for file and database contents [8, 18, 2...

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...akly consntent replication model with a read-uny/write-any style of access. Weakly consistent replication has been used previously for availability, simplicity and scalability in a variety of systems =-=[3, 7, 10, 12, 15, 19]-=-.sAnti-entropy While individual Read and Write operations are performed at a single server, clients need not confine themselves to interacting with a single server. Indeed, in a mobile computing envir...

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...s often desirable, and Bayou provides session guarantees to reduce client-observed inconsistencies when accessing different servers. The description of session guarantees has been presented elsewhere =-=[29]-=-. To support application-specific conflict detection and resolution, Bayou Writes must contain more than a typical file system write or database update. Along with the desired updates, a Bayou Write c...

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... consideration characteristics of mobile computing such as expensive connection time, frequent or occasional disconnections, and that collaborating computers may never be all connected simultaneously =-=[1, 13, 16]. Th-=-e Bayou architecture does not include the notion of a “disconnected” mode of operation because, in fact, various degrees of Mike J. Spreitzer and Carl H. Hauser Computer Science Laboratory Xerox P...

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...akly consntent replication model with a read-uny/write-any style of access. Weakly consistent replication has been used previously for availability, simplicity and scalability in a variety of systems =-=[3, 7, 10, 12, 15, 19]-=-.sAnti-entropy While individual Read and Write operations are performed at a single server, clients need not confine themselves to interacting with a single server. Indeed, in a mobile computing envir...

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...rved meetings th:~t o] erl:ip with this ume slot It expects the quer! to return m empt> wtsBayou’s dependency checks, like the version vectors and timestamps traditionally used in distributed system=-=s [12, 19, 25, 27], -=-can be used to detect Write-Write confhcts. That is, they can be used to detect when two users update the same data item without one of them first observing the other’s update. Such conflicts can be...

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...t coordination with other replicas. Every computer eventually receives updates from every other, either directly or indirectly, through a chain of pair-wise interactions. Unlike many previous systems =-=[12, 27]-=-, our goal in designing the Bayou system was not to provide transparent replicated data support for existing file system and database applications. We believe that applications must be aware that they...

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...along with Bayou’s anti-entropy protocol ensuring that servers learn of committed Writes in the order that they were committed, provides stability. In the Bayou system, we use a primary commit scheme =-=[28]-=-. That is, one server designated as the primary takes responsibility for committing updates. Knowledge of which Writes have committed and in which order they were committed then propagates to other se...

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...ocus [30] and Coda [17], have proven the value of semantic conflict detection and resolution for file directories, and several systems are exploring conflict resolution for file and database contents =-=[8, 18, 26]. -=-Bayou’s mechamsms extend this work by letting applications exploit domain-specific knowledge to achieve automatic conflict resolution at the granularity of individual update operations without compr...

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...ocus [30] and Coda [17], have proven the value of semantic conflict detection and resolution for file directories, and several systems are exploring conflict resolution for file and database contents =-=[8, 18, 26]-=-. Bayou’s mechanisms extend this work by letting applications exploit domain-specific knowledge to achieve automatic conflict resolution at the granularity of individual update operations without comp...

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...akly consntent replication model with a read-uny/write-any style of access. Weakly consistent replication has been used previously for availability, simplicity and scalability in a variety of systems =-=[3, 7, 10, 12, 15, 19]-=-.sAnti-entropy While individual Read and Write operations are performed at a single server, clients need not confine themselves to interacting with a single server. Indeed, in a mobile computing envir...

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... depends, including data items that have been read but are not being updated. Thtrs, Bayou chents can emulate the optimistic style of concurrency control employed in some distributed database systems =-=[4, 6]-=-. For example, a Write operation that installs a new program binary file might only include a dependency check of the sources, including version stamps, from which It was derived. Since the binary doe...

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... consideration characteristics of mobile computing such as expensive connection time, frequent or occasional disconnections, and that collaborating computers may never be all connected simultaneously =-=[1, 13, 16]. Th-=-e Bayou architecture does not include the notion of a “disconnected” mode of operation because, in fact, various degrees of Mike J. Spreitzer and Carl H. Hauser Computer Science Laboratory Xerox P...

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...kly consistent replication model with a read-any/write-any style of access. Weakly consistent replication has been used previously for availability, simplicity and scalability in a variety of systems =-=[3, 7, 10, 12, 15, 19]-=-.sApplication Bayou API Client Stub CLIENT Machine boundaries Read or Write SERVER Storage System Server State Anti-entropy While individual Read and Write operations are performed at a single server,...

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...turally depend on the semantics of the application. To this end, Bayou provides system support for applicatlonspecific confllct detection and resolution. Previous systems, such as Locus [30] and Coda =-=[17], -=-have proven the value of semantic conflict detection and resolution for file directories, and several systems are exploring conflict resolution for file and database contents [8, 18, 26]. Bayou’s me...

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...ured since a single storage site may not be reachable from mobile clients or within disconnected workgroups. Weak consistency is desired since any replication scheme providing one copy serializablhty =-=[6]-=-, such as reqturing clients to access a quorum of replicas or to acquire exclusive locks on data that they wish to update, yields unacceptably low write availability in par-btioned networks [5]. For t...

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... produce a revised update that logs the detected conflict in some fashion that will enable a person to resolve the conflict later. To enable manual resolution, perhaps using an interactive merge tool =-=[22]-=-, the conflicting updates must be presented to a user in a manner that allows him to understand what has happened. By convention, most Bayou data collections include an error log for unresolvable conf...

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...ablhty [6], such as reqturing clients to access a quorum of replicas or to acquire exclusive locks on data that they wish to update, yields unacceptably low write availability in par-btioned networks =-=[5]-=-. For these reasons, Bayou adopts a model in which chents can read and write to any replica without the need for explicit coordination with other rephcas. Every computer eventually receives updates fr...

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... resolving conflicts in a consistent manner across partial replicas. The next steps in the implementation will include the development of other applications, such as an e-mail reader, porting refdbms =-=[11]-=-, a widely used shared bibliographic database manager, to run on the Bayou storage system, and experimenting with wireless connectivity for servers and clients running on a laptop. 11. Acknowledgments...

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...cit coordination with other rephcas. Every computer eventually receives updates from every other, either directly or indirectly, through a chain of pair-wise interactions. Unhke many previous systems =-=[12, 27]-=-, our goal m designing the Bayou system was not to provide transparent rephcated data support for existing file system and database applications. We believe that applications must be aware that they m...

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...ocus [30] and Coda [17], have proven the value of semantic conflict detection and resolution for file directories, and several systems are exploring conflict resolution for file and database contents =-=[8, 18, 26]. -=-Bayou’s mechamsms extend this work by letting applications exploit domain-specific knowledge to achieve automatic conflict resolution at the granularity of individual update operations without compr...

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...nd executed any Writes that could possibly be ordered before the given Write. Bayou’s notion of stability is similar to that in ordered mtdticast protocols, such as those provided in the 1S1S toolki=-=t [2]. In man-=-y cases, an application can be designed with a notion of “confirmation” or “commitment” that corresponds to the Bayou notion of stability. As an example, in the Bayou meeting room scheduling a...

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...akly consntent replication model with a read-uny/write-any style of access. Weakly consistent replication has been used previously for availability, simplicity and scalability in a variety of systems =-=[3, 7, 10, 12, 15, 19]-=-.sAnti-entropy While individual Read and Write operations are performed at a single server, clients need not confine themselves to interacting with a single server. Indeed, in a mobile computing envir...

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...iant and developed in ANSI C so that the same sources run on Intel-based laptops with Linux and on our regular development platform of Sun SPARCstations with SunOS. In the current implementation, ILU =-=[14]-=-, a language-independent RPC package developed at Xerox PARC, is used for commurucation between Bayou clients and servers, as well as between servers. Server location, by both clients and other server...

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...along with Bayou’s anti-entropy protocol ensuring that servers learn of committed Writes in the order that they were committed, provides stability. In the Bayou system, we use a primary commir schem=-=e [28]-=-. That M, one server designated as the primary takes responsibihty for committing updates. Knowledge of which Writes have committed and in which order they were committed then propagates to other serv...

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...s often desirable, and Bayou provides session guarantees to reduce client-observed inconsistencies when accessing different servers. The description of session guarantees has been presented elsewhere =-=[29]-=-. To support application-specific conflict detection and resolution, Bayou Writes must contain more than a typical file system write or database update. Along with the desired updates, a Bayou Write c...