The hash history approach for reconciling mutual inconsistency

Kang, Brent Byunghoon; Wilensky, Robert L.; Kubiatowicz, John

doi:10.1109/icdcs.2003.1203518

Cited by 18 publications

(14 citation statements)

References 24 publications

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“…Until it propagates through the whole system, any update created on another replica before it hears of the resolution will be causally unrelated to the reconciliation event and will thus conflict with it. Indeed, as has been noted before [23,16], in some systems, the very same conflict might be resolved, independently, by inserting new reconciliation events at different sites, thus raising new conflicts even though the reconciled values may be identical. Most existing systems have found this potential behavior acceptable in practice-conflicts are infrequent or communication frequent enough to ensure that reconciliation events usually propagate throughout the system quickly.…”

Section: Introductionmentioning

confidence: 99%

“…A similar strategy is used in Panasync [2]. The version histories used in the Reconcile file synchronizer [15] and the Clique peer-to-peer filesystem [29], as well as Kang's hash histories [16], all represent the causal history of the system directly-storing and transmitting (hashes of) complete histories of updates -rather than deducing causal ordering from reduced representations such as clock vectors. They treat identical file contents as agreement, and keep a version history of each file (storing a SHA1 hash of the file contents after each synch operation).…”

Section: Related Workmentioning

confidence: 99%

“…If one replica, R a hears only of the partial history v, v , and the another R b hears of the complete v, v , v, then one should not equate the v on R a with the latest v on R b -else the system will converge to v , losing the final edit. [16] reduces the likelihood of this happening by using both the file contents and a "generation number" for equality tests.…”

Section: Related Workmentioning

confidence: 99%

“…Kang [16] used simulation over trace data from sourceforge.net to show that "coincident equalities" (independent updates or reconciliations that resulted in identical contents) appear to be common. The paper showed that recognizing equality as agreement substantially sped up convergence.…”

Section: Related Workmentioning

confidence: 99%

See 3 more Smart Citations

Agreeing to Agree: Conflict Resolution for Optimistically Replicated Data

Greenwald

Khanna

Kunal

et al. 2006

Lecture Notes in Computer Science

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Current techniques for reconciling disconnected changes to optimistically replicated data often use version vectors or related mechanisms to track causal histories. This allows the system to tell whether the value at one replica dominates another or whether the two replicas are in conflict. However, current algorithms do not provide entirely satisfactory ways of repairing conflicts. The usual approach is to introduce fresh events into the causal history, even in situations where the causally independent values at the two replicas are actually equal. In some scenarios these events may later conflict with each other or with further updates, slowing or even preventing convergence of the whole system.To address this issue, we enrich the set of possible actions at a replica to include a notion of explicit conflict resolution between existing events, where the user at a replica declares that one set of events dominates another, or that a set of events are equivalent. We precisely specify the behavior of this refined replication framework from a user's point of view and show that, if communication is assumed to be "reciprocal" (with pairs of replicas exchanging information about their current states), then this specification can be implemented by an algorithm with the property that the information stored at any replica and the sizes of the messages sent between replicas are bounded by a polynomial function of the number of replicas in the system.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Related Workmentioning

confidence: 99%

Section: Related Workmentioning

confidence: 99%

Section: Related Workmentioning

confidence: 99%

See 2 more Smart Citations

Agreeing to Agree: Conflict Resolution for Optimistically Replicated Data

Greenwald

Khanna

Kunal

et al. 2006

Lecture Notes in Computer Science

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“…These assumptions are incompatible with replica creation (and retirement) on distributed systems subject to arbitrary partitions, a typical mode of operation of mobile or poorly connected environments. Other approaches tackle this identification problem relying on statistical correctness [4]. These approaches, not only may lead to occasional errors (which, even very rare, may be unacceptable), but also lead to large identifiers.…”

Section: Introductionmentioning

confidence: 99%

Improving on Version Stamps

Almeida

Baquero

Fonte

On the Move to Meaningful Internet Systems 2007: OTM 2007 Workshops

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Abstract. Optimistic distributed systems often rely on version vectors or their variants in order to track updates on replicated objects. Some of these mechanisms rely on some form of global configuration or distributed naming protocol in order to assign unique identifiers to each replica. These approaches are incompatible with replica creation under arbitrary partitions, a typical operation mode in mobile or poorly connected environments. Other mechanisms assign unique identifiers relying on statistical correctness. In previous work we have introduced an update tracking mechanism that overcomes these limitations. This paper presents results from recent experimentation, that brought to surface a particular pattern of operation that results in an unforeseen, unlimited growth in space consumption. We also describe informally a new update tracking mechanism that does not exhibit this pathological growth while providing guaranteed unique identifiers for a dynamic number of replicas under arbitrary partitions and the same functionality of version vectors.

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Bounded Version Vectors

Almeida

Baquero

2004

Lecture Notes in Computer Science

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Version vectors play a central role in update tracking under optimistic distributed systems, allowing the detection of obsolete or inconsistent versions of replicated data. Version vectors do not have a bounded representation; they are based on integer counters that grow indefinitely as updates occur. Existing approaches to this problem are scarce; the mechanisms proposed are either unbounded or operate only under specific settings. This paper examines version vectors as a mechanism for data causality tracking and clarifies their role with respect to vector clocks. Then, it introduces bounded stamps and proves them to be a correct alternative to integer counters in version vectors. The resulting mechanism, bounded version vectors, represents the first bounded solution to data causality tracking between replicas subject to local updates and pairwise symmetrical synchronization.

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The hash history approach for reconciling mutual inconsistency

Abstract: We introduce the hash history mechanism for capturing dependencies among distributed replicas. Hash

Cited by 18 publications

References 24 publications

Agreeing to Agree: Conflict Resolution for Optimistically Replicated Data

Agreeing to Agree: Conflict Resolution for Optimistically Replicated Data

Improving on Version Stamps

Bounded Version Vectors

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