Concurrent Transaction Processing Research Articles

FLUID: Towards Efficient Continuous Transaction Processing in DAG-Based Blockchains

In most blockchain-based application scenarios, a complete application logic consists of multiple continuous transactions, in which the initiation of one transaction depends on the confirmation result of the previous one. This mandates that continuous transactions must be processed in the correct order. Unfortunately, existing chain-based blockchains fail to effectively support continuous transaction processing due to considerable latency in confirming continuous transactions. Recent studies shifted from chain-based blockchains to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Directed Acyclic Graph</i> (DAG) based blockchains, which reduced transaction confirmation latencies. However, DAG-based blockchains store transactions in an out-of-order manner that leads to unordered transaction processing. To address this challenge, we propose FLUID, a new DAG-based blockchain that supports continuous transaction processing while delivering high performance. The fundamental idea of FLUID is to design a transaction dependency tracking structure to ensure that continuous transactions can be processed in the correct order. FLUID utilizes a conflict resolution mechanism to provide instant confirmation and to support concurrent transaction processing with lower latencies. In addition, FLUID builds a checkpoint-based verification mechanism to achieve deterministic consensus on transaction processing results in the DAG. Extensive experiments demonstrate that our proposed FLUID can improve the throughput over state-of-the-art OHIE by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$66\%$</tex-math></inline-formula> with two orders of magnitude lower latencies.

GeoGauss: Strongly Consistent and Light-Coordinated OLTP for Geo-Replicated SQL Database

Multinational enterprises conduct global business that has a demand for geo-distributed transactional databases. Existing state-of-the-art databases adopt a sharded master-follower replication architecture. However, the single-master serving mode incurs massive cross-region writes from clients, and the sharded architecture requires multiple round-trip acknowledgments (e.g., 2PC) to ensure atomicity for cross-shard transactions. These limitations drive us to seek yet another design choice. In this paper, we propose a strongly consistent OLTP database GeoGauss with full replica multi-master architecture. To efficiently merge the updates from different master nodes, we propose a multi-master OCC that unifies data replication and concurrent transaction processing. By leveraging an epoch-based delta state merge rule and the optimistic asynchronous execution, GeoGauss ensures strong consistency with light-coordinated protocol and allows more concurrency with weak isolation, which are sufficient to meet our needs. Our geo-distributed experimental results show that GeoGauss achieves 7.06X higher throughput and 17.41X lower latency than the state-of-the-art geo-distributed database CockroachDB on the TPC-C benchmark.

A Light-Weight Distributed System for the Processing of Replicated Counter-Like Objects

In order to increase availability in a distributed system some or all of the data items are replicated and stored at separate sites. This is an issue of key concern especially since there is such a proliferation of wireless technologies and mobile users. However, the concurrent processing of transactions at separate sites can generate inconsistencies in the stored information. We have built a distributed service that manages updates to widely deployed counter-like replicas. There are many heavy-weight distributed systems targeting large information critical applications. Our system is intentionally, relatively lightweight and useful for the somewhat reduced information critical applications. The service is built on our distributed concurrency control scheme which combines optimism and pessimism in the processing of transactions. The service allows a transaction to be processed immediately (optimistically) at any individual replica as long as the transaction satisfies a cost bound. All transactions are also processed in a concurrent pessimistic manner to ensure mutual consistency.

Parallel methods for the update of partitioned inverted files

PurposeAn issue that tends to be ignored in information retrieval is the issue of updating inverted files. This is largely because inverted files were devised to provide fast query service, and much work has been done with the emphasis strongly on queries. This paper aims to study the effect of using parallel methods for the update of inverted files in order to reduce costs, by looking at two types of partitioning for inverted files: document identifier and term identifier.Design/methodology/approachRaw update service and update with query service are studied with these partitioning schemes using an incremental update strategy. The paper uses standard measures used in parallel computing such as speedup to examine the computing results and also the costs of reorganising indexes while servicing transactions.FindingsEmpirical results show that for both transaction processing and index reorganisation the document identifier method is superior. However, there is evidence that the term identifier partitioning method could be useful in a concurrent transaction processing context.Practical implicationsThere is an increasing need to service updates, which is now becoming a requirement of inverted files (for dynamic collections such as the web), demonstrating that a shift in requirements of inverted file maintenance is needed from the past.Originality/valueThe paper is of value to database administrators who manage large‐scale and dynamic text collections, and who need to use parallel computing to implement their text retrieval services.

Using semantic correctness in multidatabases to achieve local autonomy, distribute coordination, and maintain global integrity

A multidatabase poses the following four, often contradictory, requirements. First, local databases require both design autonomy to accommodate the diverse legacy nature of the local databases, and execution autonomy to ensure that local transactions are not unduly blocked by global transactions. Second, management of global transactions must be distributed to avoid bottlenecks and to tolerate failure in the global database. Third, both local and global integrity constraints must be maintained. Finally, concurrent processing of transactions requires that execution histories be correct, an objective traditionally achieved with serializability. Although alternate forms of correctness have been proposed, none of the solutions advanced to date has simultaneously achieved all four requirements. We propose a transaction processing model that uses a semantics-based notion of correctness to achieve all four requirements simultaneously for applications that satisfy a certain set of properties. The support required for global transactions forms a separate layer at each site that respects both design autonomy and execution autonomy. Global transactions are managed at each site via a successor set mechanism so that site and communication failures do not impede transactions at operating sites. Semantic correctness encompasses three properties: ensuring that local and global integrity constraints are maintained, that transactions output consistent data and that all partially executed transactions can complete. A fourth property ensures that the successor set description is a valid refinement of the specification. These four properties must be proved for applications executed by our model. We show how model checking can automate, in part, the verification of the properties.

Analytic modelling of locking protocols in database systems

The consistency of the database for concurrent transaction processing in database systems is guaranteed by concurrency control protocols which are normally implemented by two phase locking. Queuing network models are used to study two important locking protocols namely, the static and dynamic two phase locking protocols. Using simple combinatorial arguments and elementary probability theory, an efficient way of deriving expressions is provided for quantities such as the blocking delays of transactions, the probability of a lock being granted and the probability of deadlocks. Mean value analysis is then applied to the two models. The analysis is straightforward and the models are easy to understand. The analytic results show remarkable good agreement with simulation results. Some conclusions are drawn regarding the performance of locking protocols in the database systems.

Performance analysis of dynamic finite versioning schemes: storage cost vs. obsolescence

Dynamic finite versioning (DFV) schemes are an effective approach to concurrent transaction and query processing, where a finite number of consistent, but maybe slightly out-of-date, logical snapshots of the database can be dynamically derived for query access. In DFV, the storage overhead for keeping additional versions of changed data to support the logical snapshots and the amount of obsolescence faced by queries are two major performance issues. We analyze the performance of DFV, with emphasis on the trade-offs between the storage cost and obsolescence. We develop analytical models based on a renewal process approximation to evaluate the performance of DFV using M/spl ges/2 snapshots. Asymptotic closed form results for high query arrival rates are given for the case of two snapshots. Simulation is used to validate the analytical models and to evaluate the tradeoffs between various strategies for advancing snapshots when M>2. The results show that (1) the analytical models match closely with simulation; (2) storage cost and obsolescence are sensitive to the snapshot advancing strategies, and (3) usually, increasing the number of snapshots demonstrates a trade-off between storage overhead and query obsolescence. For cases with skewed accessor low update rates, a small increase in the number of snapshots beyond two can substantially reduce the obsolescence. Such a reduction in obsolescence is more significant as the coefficient of variation of the query length distribution becomes larger. Moreover, for very low update rates, a large number of snapshots can be used to reduce the obsolescence to almost zero without increasing the storage overhead.

Combining optimism and pessimism to produce high availability in distributed transaction processing

In a distributed system some or all of the data items are replicated and stored at separate nodes. This increases the availability of these items and it is then possible to complete transactions faster than in single node systems. Hovever the concurrent processing of transactions at separate nodes can generate inconsistencies in the stored information. Some mechanism must be employed to address the inconsistencies that can arise. A system has been designed that allows a transaction to be processed immediately (optimistically) at any individual node in a replicated system as long as the transaction satisfies a cost bound criterion. Such a transaction can make external responses but it does not alter the database. All transactions are also run in a global one-copy serializable manner (pessimistically) at which time their updates are committed. It may be necessary to make another external response. The transaction processing system is expressed as a simple computational model and the correctness of the system is discussed.

Performance analysis of dynamic finite versioning for concurrent transaction and query processing

In this paper, we analyze the performance of dynamic finite versioning (DFV) schemes for concurrent transaction and query processing, where a finite number of consistent snapshots can be derived for query access. We develop analytical models based on a renewal process approximation to evaluate the performance of DFV using M ≥ 2 snapshots. The storage overhead and obsolescence faced by queries are measured. Simulation is used to validate the analytical models and to evaluate the trade-offs between various starategies for advancing snapshots when M &gt; 2. The results show that (1) the analytical models match closely with simulation; 2) both the storage overhead and obsolescence are sensitive to the snapshot-advancing strategies, especially for M &gt; 2 snapshots; and (3) generally speaking, increasing the number of snapshots demonstrates a trade-off between storage overhead and query obsolescence. For cases with skewed access or low update rates, a moderate increase in the number of snapshots beyond 2 can substantially reduce the obsolescence, while the storage overhead may increase only slightly, or even decrease in some cases. Moreover, for very low update rates, a large number of snapshots demonstrates a trade-off between storage overhead and query obsolescence. For cases with skewed access or low update rates, a moderate increase in the number of snapshots beyond 2 can substantially reduce the obsolescence, while the storage overhead may increase only slightly, or even decrease in some cases. Moreover, for very low update rates, a large number of snapshots can be used to reduce the obsolescence to almost zero without increasing the storage overhead.

Analysis of database performance with dynamic locking

A detailed model of a transaction processing system with dynamic locking is developed and analyzed. Transaction classes are distinguished on the basis of the number of data items accessed and the access mode (read-only/update). The performance of the system is affected by transaction blocking and restarts, due to lock conflicts that do not or do cause deadlocks, respectively. The probability of these events is determined by the characteristics of transactions and the database access pattern. Hardware resource contention due to concurrent transaction processing is taken into account by specifying the throughput characteristic of the computer system for processing transactions when there is no data contention. A solution method based on decomposition is developed to analyze the system, and also used as the basis of an iterative scheme with reduced computational cost. The analysis to estimate the probability of lock conflicts and deadlocks is based on the mean number of locks held by transactions. These probabilities are used to derive the state transition probabilities for the Markov chain specifying the transitions among the system states. The decomposition solution method and the associated iterative scheme are shown to be more accurate than previously defined methods for dynamic locking through validation against simulation results. Several important conclusions regarding the behavior of dynamic locking systems are derived from parametric studies.

Clarification of two phase locking in concurrent transaction processing

The authors propose a formal definition of the two-phase locking class derived from the semantic description of the two-phase locking protocol, and prove that this definition is equivalent to that given by C.H. Papadimitriou (1979). They present: (1) a precise definition of the two phase locking; (2) a clarification of the occurrence and the order of all events such as lock points, unlock points, read operations, and write operations of conflicting transactions; and (3) by relaxing some conditions in the given definition, the derivation of a new class called restricted-non-two-phase locking (RN2PL), which is a superset of the class two-phase locking (2PL) but a subset of the class D-serializable (DSR) given by Papadimitriou.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A theory of reliability in database systems

Reliable concurrent processing of transactions in a database system is examined. Since serializability, the conventional concurrency control correctness criterion, is not adequate in the presence of common failures, another theory of correctness is proposed, involving the concepts of commit serializability, recoverability, and resiliency.

Perfornance Study of Two Phase Locking in Single-Site Database Systems

Many database systems guarantee the consistency of the database for concurrent transaction processing by a standard locking protocol called two phase locking. The performance of such systems is dependent on various factors, among which are the choices of locking granularity (the amount of data controlled by a single lock) and degree of multiprogramming (the maximum number of transactions allowed to run concurrently in the system). Previous simulation and experimental studies on such systems suggest that the choices are dependent on the properties of the application.