Prefetching techniques for client server object-oriented database systems

The performance of many object-oriented database applications suffers from the page fetch latency which is determined by the expense of disk access. In this work we suggest several prefetching techniques to avoid, or at least to reduce, page fetch latency. In practice no prediction technique is perfect and no prefetching technique can entirely eliminate delay due to page fetch latency. Therefore we are interested in the trade-off between the level of accuracy required for obtaining good results in terms of elapsed time reduction and the processing overhead needed to achieve this level of accuracy. If prefetching accuracy is high then the total elapsed time of an application can be reduced significantly otherwise if the prefetching accuracy is low, many incorrect pages are prefetched and the extra load on the client, network, server and disks decreases the whole system performance. Access pattern of object-oriented databases are often complex and usually hard to predict accurately. The ..

An Adaptable Multithreaded Prefetching Technique for Client-Server Object Bases

this paper, we examine the way in which prefetching can exploit parallelism. Prefetching has been studied before in many areas of computing such as operating systems, microprocessor design, compiler construction, the world wide web and databases. Although prefetching has been studied for a long time, the problem prefetching is facing has changed over the years as a result of technology advances. Fig. 1 shows the performance/price development of semiconductor memories and magnetic disks. There is a two-order of magnitude gap in access time between memory and disks. Memory access is faster and the rate of improvement is also higher. The prices of memory are falling which makes database N. Knafla / An Adaptable Multithreaded Prefetching Technique 3 caches cheaper and buffer replacement less of a problem. Prices of disks are also falling dramatically which is good for cheap secondary storage, allowing increased use of RAIDs. CPU performance improves at an even higher rate than memory (fig. 2). CPU is doubling its performance every 18 months whereas disk retrieval time only improves about 5% per year. Memory access time improves at about 10 to 12% per year. Client workstations will become powerful multi-processors machines with high speed CPUs, most of which will tend to be idle most of the time. 1 10 100 1000 1980 1985 1990 199

Analysing Object Relationships to Predict Page Access for Prefetching

We present a new approach to predicting page accesses to facilitate prefetching persistent objects in a client/server computing environment. The relationships between persistent objects are modelled by a discrete-time Markov Chain, which allowed us to use a method called hitting times to compute the page access probability and the mean time to access a page. If the probability of a page is higher than a threshold defined by cost/benefit parameters then the page is a candidate for prefetching. To determine the prefetching threshold we consider various cost parameters to compare the benefit of a correct prefetch with the cost of an incorrect prefetch. In addition, we compute the best possible time to start the prefetch operation. We incorporated this prefetching algorithm into the EXODUS storage manager, and used the timing results in a simulation. Keywords: prefetching, persistent object stores, object-oriented databases, discrete-time Markov Chains, hitting times and hitting probabil..

A Prefetching Technique for Object-Oriented Databases

We present a new prefetching technique for objectoriented databases which exploits the availability of multiprocessor client workstations. The prefetching information is obtained from the object relationships on the database pages and is stored in a Prefetch Object Table. This prefetching algorithm is implemented using multithreading. In the results we show the theoretical and empirical benefits of prefetching. The benchmark tests show that multithreaded prefetching can improve performance significantly for applications where the object access is reasonably predictable. Keywords: prefetching, distribution, object-oriented databases, performance analysis, multithreading, application access pattern, storage management 1 Introduction Two industry trends in the performance/price ratio of hardware systems have implications for the efficient implementation of object-oriented database management systems (OODBMSs) in a client/server computing environment. Firstly, the continuing fall in pric..

Page versus Object Prefetching: A Performance Evaluation

In this report we compare the performance of a prefetching page server system with a prefetching object server system. We simulate the object access pattern by assigning transition probabilities to the object relationships. According to the transition probabilities we compute the access probability of pages and objects. We designed several prefetching techniques for a prefetching page server and a prefetching object server. We compared the performance of the prefetching techniques in a simulation

Speed Up Your Database Client with Adaptable Multithreaded Prefetching

In many client/server object database applications, performance is limited by the delay in transferring pages from the server to the client. We present a prefetching technique that can avoid this delay, especially where there are several database servers. Part of the novelty of this approach lies in the way that multithreading on the client workstation is exploited, in particular for activities such as prefetching and flushing dirty pages to the server. Using our own complex object benchmark we analyze the performance of the prefetching technique with multiple clients, multiple servers and different buffer pool sizes. 1 Introduction Much of the research and development effort in highperformance database systems has focused on exploiting parallel computing on the database server platform. However, the falling prices of shared-memory multiprocessors makes such machines feasible as client hosts. This raises the question of how a multiprocessor client machine can be exploited to improve d..