Dr. Dobb's Journal - May 2008 - (Page 40)

d05gor_p3db 3/13/08 9:09 AM Page 40 State of the Art KERNEL-MODE DATABASES continued from page 38 cause too much impact on the system. Data management can’t monopolize or extensively use any of the system’s resources, increase interrupt latencies, or noticeably affect overall system responsiveness to outside events. User Program Database API User mode Kernal mode Database “proxy” Database repository Database runtime Network Driver Database runtime Network Driver It has to provide simultaneous access to data for all parts of the system, including from multiple user-mode processes and kernel threads. Further, this data access must include both write/read access and be efficient enough to avoid stalling the kernel. The kernel-mode database is made available to user-mode applications through a set of public interfaces implemented via system calls; see Figure 1. For the kernel-mode database integration in Figure 1 to work, the kernel-based database runtime must address many of the same challenges as kernel-based programs and embedded systems generally. The issues and solutions involved in deploying a database in kernel space are also highly applicable to device drivers, filesystems, and other kernel modules: • To provide multithreaded, simultaneous data access, the database runtime must use synchronization mechanisms. Nearly every driver requires synchronization mechanisms as well, because Figure 1: Public interfaces. this function is needed for any shared data to be accessed by multiple threads, unless this access is read-only. Synchronization is also required when a set of operations must be performed atomically, inside a transaction. OS synchronization mechanisms can cause performance bottlenecks. To improve locking performance, the kernel-mode database uses locks based on the atomic exchange instructions provided by many CPU architectures. When the nature of the resource requires mutual exclusion between threads, the database runtime claims resources only for a short time. Thus the database locks use a low-overhead spinlock-based mechanism that protects the resource. • Efficient memory use is often a key to application performance, especially in the kernel where the nonpaged memory pool is limited and frequent paging could increase kernel latencies. To address this, in-memory databases often use a number of custom allocation algorithms to take advantage of problem-specific allocation patterns, such as infrastructure for the data layout, internal database runtime heap management, and so on. Download a proven, cross-platform database alternative • Unmatched performance in enterprise systems, desktop deployments, and embedded devices for over 25 years. • Simplified framework for rapid development of data-driven applications including graphical tools to speed your development and monitor critical metrics of the database engine. • Free development and free deployment in non-commercial environments. • Flexibility to use ISAM and SQL API’s within the same application. • Sophisticated feature set including 64-bit support, memory files, ADO.NET, LINQ, C#, VCL, and dbExpress. • Cross Platform support including Windows, UNIX, Linux, Mac OS X, and more. • OEM Database Engine simplifies your deployment with a single executable and flexible licensing options. Prove it to yourself in six minutes. 40 Download today! www.faircom.com Dr. Dobb’s Journal l www.ddj.com l May 2008 http://www.faircom.com http://www.faircom.com http://www.ddj.com

Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - May 2008

Dr. Dobb's Journal - May 2008 Contents Friday Night Fish Fry Alia Vox Developer Diaries Software Development Goes to the Movies Cat: A Functional Stack-Based Little Language Mojax: Mobile Ajax Framework Kernel-Mode Databases Getting Better Search Results Effective Concurrency The Agile Edge

Dr. Dobb's Journal - May 2008

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