High Concurrency for Continuously Evolving OODBMS

For next generation information systems, concurrency control mechanisms are required to handle high level abstract operations and to meet high throughput demands. The currently available single level concurrency control mechanisms for reads and writes are inadequate for future complex information systems. In this paper, we will present a new multilevel concurrency protocol that uses a semantics-based notion of conflict, which is weaker than commutativity, called recoverability . Further, operations are scheduled according to relative conflict , a conflict notion based on the structure of operations. Performance evaluation via extensive simulation studies show that with our multilevel concurrency control protocol, the performance improvement is significant when compared to that of a single level two-phase locking based concurrency control scheme or to that of a multilevel concurrency control scheme based on commutativity alone. Further, simulation studies show that our new multilevel concurrency control protocol performs better even with resource contention.

Collaborative virtual environment for product design occurs between people and often involves 3D objects. Fruitful cooperation is helped by natural and intuitive way of communication and interaction, for which responsiveness and consistency are leading factors. In order to guarantee consistency and improve responsiveness, a novel concurrency control scheme is first proposed. In our scheme, non-exclusive concurrent manipulations are merged so as to undo a small quantity of manipulations rather than all the operations triggered by users who are not granted, therefore, a majority of concurrent operations are collision-free and executed immediately to maximize responsiveness. Moreover, notification and visual indicator mechanism are used to avoid unnecessary concurrency collision. The implementation of collaborative virtual environment named VRCAD is then introduced in detail, including system architecture, concurrency control strategy and communication facilities. Experiment and practice show that our concurrency control scheme is effective and efficient for collaborative virtual environment involving 3D objects.

Proposes a hybrid concurrency control scheme which can alleviate the effects of frequent disconnections and bandwidth limitations in mobile computing environments. If a transaction in a mobile host executes only read operations, our concurrency control scheme is the same as the optimistic concurrency control scheme based on the timestamp history. Otherwise, if it executes write operations, the write set has to be sent to a fixed host during the execution phase. If a disconnection from the mobile host occurs, the fixed host performs a pre-validation of the write set. As a result of this pre-validation, if conflicts are detected, the transaction is aborted. Otherwise, we use the locking method called weak lock. Our scheme reduces the number of aborts and the validation time without message overheads.

Multicore in-memory databases often rely on traditional con- currency control schemes such as two-phase-locking (2PL) or optimistic concurrency control (OCC). Unfortunately, when the workload exhibits a non-trivial amount of contention, both 2PL and OCC sacrifice much parallel execution op- portunity. In this paper, we describe a new concurrency control scheme, interleaving constrained concurrency con- trol (IC3), which provides serializability while allowing for parallel execution of certain conflicting transactions. IC3 combines the static analysis of the transaction workload with runtime techniques that track and enforce dependencies among concurrent transactions. The use of static analysis simplifies IC3's runtime design, allowing it to scale to many cores. Evaluations on a 64-core machine using the TPC- C benchmark show that IC3 outperforms traditional con- currency control schemes under contention. It achieves the throughput of 434K transactions/sec on the TPC-C bench- mark configured with only one warehouse. It also scales better than several recent concurrent control schemes that also target contended workloads.

A transaction model for multidatabase system (MDBS) applications in which global subtransactions may be either compensatable or retriable is presented. In this model compensation and retrying are used for recovery purposes. However, since such executions may no longer consist of atomic transactions, a correctness criterion that ensures that transactions see consistent database states is necessary. A commit protocol and a concurrency control scheme that ensures that all generated schedules are correct are also presented. The commit protocol eliminates the problem of blocking, which is characteristics of the standard 2PC protocol. The concurrency control protocol can be used in any MDBS environment irrespective of the concurrency control protocol followed by the local DBMSs in order to ensure serializability. >

With ever-increasing volume and heterogeneity of data, advent of new specialized compute engines, and demand for complex use cases, large-scale data systems require a performant catalog system that can satisfy diverse needs. We argue that existing solutions, including recent lakehouse storage formats, have fundamental limitations and that there is a strong motivation for a specialized database engine, dedicated to serve as the catalog. We present the design and implementation of TreeCat , a database engine that features a hierarchical data model with a path-based query language, a storage format optimized for efficient range queries and versioning, and a correlated scan operation that enables fast query execution. A key performance challenge is supporting concurrent read and write operations from many different clients while providing strict consistency guarantees. To this end, we present a novel MVOCC (multi-versioned optimistic concurrency control) protocol that guarantees serializable isolation. We conduct a comprehensive experimental evaluation comparing our concurrency control scheme with prior techniques, and evaluating our overall system against Hive Metastore, Delta Lake, and Iceberg.

Concurrency control schemes for OODBMSs used in the area of performance-critical applications should increase the degree of concurrency and decrease locking overhead in order to offer maximum throughput and minimum response time. However, most commercially available OODBMSs use conventional concurrency control schemes which never exploit the rich semantics of object-oriented data model, so that they fail to offer better performance. In this paper, we propose a concurrency control scheme for OODBMSs, called ISMGL, that not only exploits semantics regarding methods to enhance the concurrency degree, but also utilizes multigranularity locking rules to decrease locking overhead. The novel aspect of ISMGL is that it combines conventional multigranularity locking and nested transaction model with utilizing commutativity of methods. Our concurrency control scheme is applicable for realistic OODBMSs in the presence of complex objects with shared subobjects.

In OLTP systems, serializability is a key property for executions; without this, integrity constraints on data can be violated due to concurrent activities. The serializability property can be guaranteed through the implementation of concurrency control mechanisms such as strict 2-phase locking (S2PL). However, modern OLTP systems are expected to execute millions of transactions concurrently and mechanisms such as S2PL do not scale to handle this level of concurrency. Thus, to get better performance, programmers may choose different isolation levels, rather than the default ones, which are more suitable for their applications. Due to differing requirements, transaction aborts may be high. Thus, this paper investigates the correctness of mixing transactions with different isolation levels and extends the mixing theorem introduced by Adya et al. The extension investigates the correctness of mixing transactions with different isolation levels, especially when optimistic concurrency control (OCC) schemes are used which are not the main focus of the theorem. We thus propose OCC2T, an OCC-based algorithm that is designed to improve the performance of DBMS by decreasing the abort rate of transactions and enhancing mixing transactions with different isolation levels. Our results show that OCC2T is able to reduce the abort rate in highly contended workloads by almost 5x over other algorithms.

On Long-duration CAD Transactions

An adaptable constrained locking protocol for high data contention environments: correctness and performance

Concurrency control (CC) algorithms guarantee the correctness and consistency criteria for concurrent execution of a set of transactions in a database. A precondition that is seen in many CC algorithms is that the writeset (WS) and readset (RS) of transactions should be known before the transaction execution. However, in real operational environments, we know the WS and RS only for a fraction of transaction set before execution. However, optional knowledge about WS and RS of transactions is one of the advantages of the proposed CC algorithm in this paper. If the WS and RS are known before the transaction execution, the proposed algorithm will use them to improve the concurrency and performance. On the other hand, the concurrency control algorithms often use a specific static or dynamic equation in making decision about granting a lock or detection of the winner transaction. The proposed algorithm in this paper uses an adaptive resonance theory (ART)-based neural network for such a decision making. In this way, a parameter called health factor (HF) is defined for transactions that is used for comparing the transactions and detecting the winner one in accessing the database objects. HF is calculated using ART2 neural network. Experimental results show that the proposed neural-based CC (NCC) algorithm increases the level of concurrency by decreasing the number of aborts. The performance of proposed algorithm is compared with strict two-phase locking (S2PL) algorithm, which has been used in most commercial database systems. Simulation results show that the performance of proposed NCC algorithm, in terms of number of aborts, is better than S2PL algorithm in different transaction rates.

Developing concurrent applications is not a trivial task. As programs grow larger and become more complex, advanced concurrency control mechanisms are needed to ensure that application consistency is not compromised. Managing mutual exclusion on a per‐object basis is not sufficient to guarantee isolation of sets of semantically‐related actions. In this paper, we consider ‘atomic blocks’, a simple and lightweight concurrency control paradigm that enables arbitrary blocks of code to access multiple shared objects in isolation. We evaluate various strategies for implementing atomic blocks in Java, in such a way that concurrency control is transparent to the programmer, isolation is preserved, and concurrency is maximized. We discuss these concurrency control strategies and evaluate them in terms of complexity and performance. Copyright © 2002 John Wiley & Sons, Ltd.

Indexes are used in database management systems as a mechanism to speed up data retrieval. A good index structure should ensure that the data access through it is efficient and transactional. For one dimensional data, the B+-tree and its variants, such as the Blink-Tree and the π,-tree, are used widely because of their good query performance and concurrency control and recovery. However, structures for multidimensional data, despite the intense research for more than two decades, have not been so successful. Very few of the many proposed structures are implemented in commercial databases. For those that have been used, users are confronted with either poor performance or low concurrency. We proposed a new spatial access method called the Spatial C-Tree. Our approach extends the C-Tree framework, which provides efficient concurrency control and robust recovery mechanism. We have implemented the Spatial C-Tree and compared it with several R-Tree variants. Our performance results show that the Spatial C-Tree performs very well in terms of insertion and exact match queries with various data sets. Our range query performance in some cases is comparable to the R-Tree variants and in other cases are outperformed by the R-Tree variants. We have identified possible improvements over the range query performance. The potential improvement on the range query performance and the high concurrency guarantee make the Spatial C-Tree a promising access method for spatial data.

Starvation-free secure multiversion concurrency control

The LogicBlox system aims to reduce the complexity of software development for modern applications which enhance and automate decision-making and enable their users to evolve their capabilities via a ``self-service'' model. Our perspective in this area is informed by over twenty years of experience building dozens of mission-critical enterprise applications that are in use by hundreds of large enterprises across industries such as retail, telecommunications, banking, and government. We designed and built LogicBlox to be the system we wished we had when developing those applications. In this paper, we discuss the design considerations behind the LogicBlox system and give an overview of its implementation, highlighting innovative aspects. These include: LogiQL, a unified and declarative language based on Datalog; the use of purely functional data structures; novel join processing strategies; advanced incremental maintenance and live programming facilities; a novel concurrency control scheme; and built-in support for prescriptive and predictive analytics.