Transactional Workloads Research Articles

Real-time index concurrency control

Real-time database systems are expected to rely heavily on indexes to speed up data access and, thereby, help more transactions meet their deadlines. Accordingly, high- performance index concurrency control (ICC) protocols are required to prevent contention for the index from becoming a bottleneck. In this paper, we develop real-time variants of a representative set of classical B-tree ICC protocols and, using a detailed simulation model, compare their performance for real-time transactions with firm deadlines. We also present and evaluate a new real-time ICC protocol called GUARD-link that augments the classical B-link protocol with a feedback-based admission control mechanism. Both point and range queries, as well as the undos of the index actions of aborted transactions are included in the scope of our study. The performance metrics used in evaluating the ICC protocols are the percentage of transactions that miss their deadlines and the fairness with respect to transaction type and size. Our experimental results show that the performance characteristics of the real-time version of an ICC protocol could be significantly different from the performance of the same protocol in a conventional (nonreal-time) database system. In particular, B-link protocols, which are reputed to provide the best overall performance in conventional database systems, perform poorly under heavy real-time loads. The new GUARD-link protocol, however, although based on the B-link approach, delivers the best performance (with respect to all performance metrics) for a variety of real-time transaction workloads, by virtue of its admission control mechanism. In fact, GUARD-link provides close to ideal fairness in most environments. These and other results presented here represent the first work in the area of real-time index concurrency control.

Cache sampling by sets

An approach to workload sampling in which, instead of selection of memory references based on the time parameter, sample decisions are based on where the cache is accessed. More specifically, the sampling heuristics are focused on analysis for set-associative caches. The validity of the heuristics is supported with empirical data. Four sampling policies are discussed, and simulation results based on a commercial database transaction workload are presented. Observations from simulation studies with SPEC 1.0 uniprogram benchmarks are also described. An environment in which congruence class sampling may be useful is illustrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Data access scheduling in firm real-time database systems

A major challenge addressed by conventional database systems has been to efficiently implement the transaction model, which provides the properties of atomicity, serializability, and permanence. Real-time applications have added a complex new dimension to this challenge by placing deadlines on the response time of the database system. In this paper, we examine the problem of real-time data access scheduling, that is, the problem of scheduling the data accesses of real-time transactions in order to meet their deadlines. In particular, we focus on firm deadline real-time database applications, where transactions that miss their deadlines are discarded and the objective of the real-time database system is to minimize the number of missed deadlines. Within this framework, we use a detailed simulation model to compare the performance of several real-time locking protocols and optimistic concurrency control algorithms under a variety of real-time transaction workloads. The results of our study show that in moving from the conventional database system domain to the real-time domain, there are new performance-related forces that come into effect. Our experiments demonstrate that these factors can cause performance recommendations that were valid in a conventional database setting to be significantly altered in the corresponding real-time setting.

Approximate MVA solutions with fixed throughput classes

Transaction (open) type workloads are often used in approximating computer system workloads which are actually closed because open workloads provide reasonable estimates in many cases and their solutions are straight-forward. We have found that their use can distort the results for many workloads in a multiclass queueing network model of a computer system. We have replaced transaction workloads with what we call fixed class workloads. We present an approximate algorithm based on MVA that represents a class with a given throughput by a corresponding terminal or batch class, which we call a fixed class workload. We solve for the closed population required to deliver the requested throughput. We also present techniques for overcoming problems encountered in the solution of some fixed class models.

A queueing network model for a distributed database testbed system

A queuing network model for analyzing the performance of a distributed database testbed system with a transaction workload is developed. The model includes the effects of the concurrency control protocol (two-phase locking with distributed deadlock detection), the transaction recovery protocol (write-ahead logging of before-images), and the commit protocol (centralized two-phase commit) used in the testbed system. The queuing model differs from previous analytical models in three major aspects. First, it is a model for a distributed transaction processing system. Second, it is more general and integrated than previous analytical models. Finally, it reflects a functioning distributed database testbed system and is validated against performance measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A performance comparison of multi-micro and mainframe database architectures

Database machine architectures consisting of multiple microprocessors or mini-computers are attracting wide attention. There have been several proposals and prototypes (see, e.g., DeWitt, Gerber, G...