We present PoWerStore, the first efficient robust storage protocol that achieves optimal latency without using digital signatures. PoWerStore's robustness comprises tolerating asynchrony, maximum number of Byzantine storage servers, any number of Byzantine readers and crash-faulty writers, and guaranteeing wait-freedom and linearizability of read write operations. PoWerStore's efficiency stems from combining lightweight authentication, erasure coding and metadata write-backs where readers write-back only metadata to achieve linearizability. At the heart of PoWerStore are Proofs of Writing (PoW): a novel storage technique based on lightweight cryptography. PoW enable reads and writes in the single-writer variant of PoWerStore to have latency of 2 rounds of communication between a client and storage servers in the worst-case (which we show optimal). We further present and implement a multi-writer PoWerStore variant featuring 3-round writes reads where the third read round is invoked only under active attacks, and show that it outperforms existing robust storage protocols, including crash-tolerant ones.
A seminal crash-tolerant read write storage implementation assuming a majority of correct processes was presented in @cite_13 . In the original single-writer variant of @cite_13 , read operations always take 2 rounds between a client and servers with write-backs in the second round. On the other hand all write operations complete in a single round; in the multi-writer variant @cite_5 , the second write round is necessary. Server state modifications by readers introduced by @cite_13 are unavoidable; namely, @cite_23 showed a @math lower bound on the number of servers that a reader has to modify in any wait-free linearizable storage. However, robust storage implementations differ in the strategy employed by readers: in some protocols readers write-back data (e.g., @cite_13 @cite_47 @cite_42 @cite_37 @cite_49 @cite_33 ) whereas in others readers only write metadata to servers (e.g., @cite_23 @cite_18 @cite_41 ).
@cite_37 @cite_18 @cite_33 @cite_41 @cite_42 @cite_23 @cite_49 @cite_5 @cite_47 @cite_13
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We study the time-complexity of robust atomic read write storage from fault-prone storage components in asynchronous message-passing systems. Robustness here means wait-free tolerating the largest possible number t of Byzantine storage component failures (optimal resilience) without relying on data authentication. We show that no single-writer multiple-reader (SWMR) robust atomic storage implementation exists if (a) read operations complete in less than four communication round-trips (rounds), and (b) the time complexity of write operations is constant. More precisely, we present two lower bounds. The first is a read lower bound stating that three rounds of communication are necessary to read from a SWMR robust atomic storage. The second is a write lower bound, showing that Ω(log(t)) write rounds are necessary to read in three rounds from such a storage. Applied to known results, our lower bounds close a fundamental gap: we show that time-optimal robust atomic storage can be obtained using well-known transformations from regular to atomic storage and existing time-optimal regular storage implementations. A citing sentence is one that appears in a scientific article and cites previous work. Citing sentences have been studied and used in many applications. For example, they have been used in scientific paper summarization, automatic survey generation, paraphrase identification, and citation function classification. Citing sentences that cite multiple papers are common in scientific writing. This observation should be taken into consideration when using citing sentences in applications. For instance, when a citing sentence is used in a summary of a scientific paper, only the fragments of the sentence that are relevant to the summarized paper should be included in the summary. In this paper, we present and compare three different approaches for identifying the fragments of a citing sentence that are related to a given target reference. Our methods are: word classification, sequence labeling, and segment classification. Our experiments show that segment classification achieves the best results. This paper establishes tight bounds on the best-case time-complexity of distributed atomic read write storage implementations that tolerate worst-case conditions. We study asynchronous robust implementations where a writer and a set of reader processes (clients) access an atomic storage implemented over a set of 2t+b+1 server processes of which t can fail: b of these can be malicious and the rest can crash. We define a lucky operation (read or write) as one that runs synchronously and without contention. It is often argued in practice that lucky operations are the most frequent. We determine the exact conditions under which a lucky operation can be fast, namely expedited in onecommunication round-trip with no data authentication. We show that every lucky write (resp., read) can be fast despite fw(resp., fr) actual failures, if and only if fw + fr t-b. This paper investigates time-efficient implementations of atomic read-write registers in message-passing systems where the number of readers can be unbounded. In particular we study the case of a single writer, multiple readers, and S servers, such that the writer, any subset of the readers, and up to t servers may crash. A recent result of [P. Dutta, R. Guerraoui, R.R. Levy, A. Chakraborty, How fast can a distributed atomic read be? In: Proceedings of the 23rd ACM Symposium on Principles of Distributed Computing, 2004, pp. 236-245] shows how to obtain fast implementations in which both reads and writes complete in one communication round-trip, under the constraint that the number of readers is less than St-2, where t