fastdb简介

Introduction

FastDB is a highly efficient main memory database system with realtime capabilities and convenient C++ interface. FastDB doesn't support a client-server architecture and all applications using a FastDB database should run at the same host. FastDB is optimized for applications with dominated read access pattern. High speed of query execution is provided by the elimination of data transfer overhead and a very effective locking implementation. The Database file is mapped to the virtual memory space of each application working with the database. So the query is executed in the context of the application, requiring no context switching and data transfer. Synchronization of concurrent database access is implemented in FastDB by means of atomic instructions, adding almost no overhead to query processing. FastDB assumes that the whole database is present in RAM and optimizes the search algorithms and structures according to this assumption. Moreover, FastDB has no overhead caused by database buffer management and needs no data transfer between a database file and buffer pool. That is why FastDB will work significantly faster than a traditional database with all data cached in buffers pool.

FastDB supports transactions, online backup and automatic recovery after system crash. The transaction commit protocol is based on a shadow root pages algorithm, performing atomic update of the database. Recovery can be done very fast, providing high availability for critical applications. Moreover, the elimination of transaction logs improves the total system performance and leads to a more effective usage of system resources.

FastDB is an application-oriented database. Database tables are constructed using information about application classes. FastDB supports automatic scheme evaluation, allowing you to do changes only in one place - in your application classes. FastDB provides a flexible and convenient interface for retrieving data from the database. A SQL-like query language is used to specify queries. Such post-relational capabilities as non-atomic fields, nested arrays, user-defined types and methods, direct interobject references simplifies the design of database applications and makes them more efficient.

Although FastDB is optimized in the assumption that database as a whole fits into the physical memory of the computer, it is also possible to use it with databases, the size of which exceeds the size of the physical memory in the system. In the last case, standard operating system swapping mechanisms will work. But all FastDB search algorithms and structures are optimized under the assumption of residence of all data in memory, so the efficiency for swapped out data will not be very high.

FastDb是高效的内存数据库系统，具备实时能力及便利的C++接口。FastDB不支持client-server架构因而所有使用FastDB的应用程序必须运行在同一主机上。FastDB针对应用程序通过控制读访问模式作了优化。通过降低数据传输的开销和非常有效的锁机制提供了高速的查询。对每一个使用数据库的应用数据库文件被影射到虚拟内存空间中。因此查询在应用的上下文中执行而不需要切换上下文以及数据传输。fastdb中并发访问数据库的同步机制通过原子指令实现，几乎不增加查询的开销。fastdb假定整个数据库存在于RAM中，并且依据这个假定优化了查询算法和接口。此外，fastdb没有数据库缓冲管理开销，不需要在数据库文件和缓冲池之间传输数据。这就是fastdb运行速度明显快于把数据放在缓冲池中的传统数据库的原因。

fastdb支持事务、在线备份以及系统崩溃后的自动恢复。事务提交协议依据一个影子根页面算法来自动更新数据库。恢复可以执行得非常快，为临界应用提供了高可用性。此外，取消事务日志改进了整个系统的性能，并且使得可以更有效的利用系统资源。

fastdb是一个面向应用的数据库，数据库表通过应用程序的类信息来构造。fastdb支持自动的模式评估，使你可以只需要在一个地方更改-你的应用程序的类。fastdb提供一个灵活方便的接口来从数据库中获取数据。使用一个类SQL的查询语言进行指定的查询。通过一些后关系特性如非原子字段，嵌套数组，用户定义类型和方法，对象间直接引用简化了数据库应用程序的设计并使之更有效率。

尽管fastdb的优化是立足于假定整个数据库配置在计算机的物理内存中，但是也有可能出现使用的数据库的大小超过了系统物理内存的大小的情况，在这种情况下标准的操作系统交换机制就会工作。但是整个fastdb的搜索算法和结构是建立在假定所有的数据都存在于内存中的，因此数据换出的效率不会很高。