Bringing modular concurrency control to the next level

Database users face a tension between ease-of-programming and high performance: ACID transactions can greatly simplify the programming effort of database applications by providing four useful properties—atomicity, consistency, isolation, and durability, but enforcing these properties can degrade performance. This dissertation eases this tension by improving the performance of ACID transactions for scenarios where data contention is the bottleneck. The approach that we take is federating concurrency control (CC) mechanisms. It is based on the observation that any single CC mechanism is bound to make trade-offs that cause it to perform well in some cases but poorly in others. A federation opens the opportunity of applying each mechanism only to the set of transactions or workloads where it shines, while maintaining isolation. In particular, this work builds upon Modular Concurrency Control (MCC), a recent technique that federates CCs by partitioning transactions into groups, and by applying different CC mechanisms in each group. This dissertation addresses two critical shortcomings in the current embodiment of MCC. First, cross-group data conflicts are handled with a single, unoptimized CC mechanism that can significantly limit performance. Second, configuring MCC is a complex task, which runs counter to MCC’s purpose: to improve performance without sacrificing ease-of-programming. To address these problems, this dissertation presents Tebaldi, a new transactional database that brings Modular Concurrency Control to the next level, both figuratively and literally. Tebaldi introduces a new, hierarchical model to MCC that partitions transactions recursively to compose CC mechanisms in a multi-level tree. This model increases flexibility in federating CC mechanisms, which is the key to realizing the performance potential of federation. Tebaldi reduces configuration complexity by managing the MCC federation automatically: it can detect performance issues in the current workload in real-time, and automatically adjusts its configuration to improve its performance.Computer Science

A comparative study of transaction management services in multidatabase heterogeneous systems

Multidatabases are being actively researched as a relatively new area in which many aspects are not yet fully understood. This area of transaction management in multidatabase systems still has many unresolved problems. The problem areas which this dissertation addresses are classification of multidatabase systems, global concurrency control, correctness criterion in a multidatabase environment, global deadlock detection, atomic commitment and crash recovery. A core group of research addressing these problems was identified and studied. The dissertation contributes to the multidatabase transaction management topic by introducing an alternative classification method for such multiple database systems; assessing existing research into transaction management schemes and based on this assessment, proposes a transaction processing model founded on the optimal properties of transaction management identified during the course of this research.ComputingM. Sc. (Computer Science

Practical cross-engine transactions in dual-engine database systems

With the growing DRAM capacity and core count in modern servers, database systems are becoming increasingly multi-engine to feature a heterogeneous set of engines. In particular, a memory-optimized engine and a conventional storage-centric engine may coexist to satisfy various application needs. However, handling cross-engine transactions that access more than one engine remains challenging in terms of correctness, performance and programmability. This thesis describes Skeena, an approach to cross-engine transactions with proper isolation guarantees and low overhead. Skeena adapts and integrates past concurrency control theory to provide a complete solution to supporting various isolation levels in dual-engine systems, and proposes a lightweight transaction tracking structure that captures the necessary information to guarantee correctness with low overhead. Evaluation on a 40-core server shows that Skeena only incurs minuscule overhead for cross-engine transactions, without penalizing single-engine transactions

Supporting Altruistic Protocol in Multidatabase System

Computer Science