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JetSun — Tue, 20 Jun 2006 10:46:00 GMT

摘要: SQlite的发展简�? SQLite��实是个不错的东西，本来不才�Q�目前还没有能得其精髓。在研究中。先到它官方�|�站把它的发展变化脓�q�来�Q�这也是它迅速发展的一个痕�q�V�? 2006 June 6 (3.3.6) Play... 阅读全文

JetSun 2006-06-20 18:46 发表评论

�Ҏ��和局限�?��译)

JetSun — Wed, 31 May 2006 14:25:00 GMT

Features and Limitations

�Ҏ��和局限�?/font>

In this section we will look at the key features of SQLite and some of its limitations. The nature of SQLite makes it an ideal choice for quite a number of tasks, but it's not suitable for everything.

在本部分我们��要看一下SQLite关键�Ҏ��和它的一些局限性。SQLite的本质��它成��多�Q务的理想选择�Q�但它�ƈ不适合所有的斚w��?br />
It is important to decide whether SQLite or any other database engine for that matteris the right choice for your application before committing to a particular technology.

在�ؓ你的应用��定一个特�D�的技术之前，军_��选择使用SQLite或者其它的��M��数据库引擎作是非帔R��要的�?br />

Speed

速度

SQLite is extremely efficient, benefiting from a highly optimized internal architecture and a small memory footprint. Because SQLite is not a client/server database, the overheads of running a database daemon and socket communication are eliminated.

SQLite 非常高效�Q�这得益于高度优化的内部�l�构和很��的内存需求。因为SQLite 不是一个客��L��/服务器类型的数据库，�q�行一个数据库�q�程和套接字通信的开销被消除了�?br />
The published speed comparison at http://www.sqlite.org/speed.html compares SQLite to both MySQL and PostgreSQL. It finds that SQLite can perform up to 20 times faster than PostgreSQL and more than twice as fast as MySQL for common operations.

�?/font> http://www.sqlite.org/speed.html 上的发表了它和MySQL和PostgreSQL速度�Ҏ��。对比表明，SQLite在执行普通操作的时候速度比PostgreSQL�?0倍，是MySQL的两倍�?/font>

These tests were performed with default installations of each database, and although it is possible to tune the MySQL and PostgreSQL servers for slightly better performance in a given environment, SQLite does not require any such optimization.

�q�个是在每个数据库的默认安装情况下测试的�Q�尽��在�l�定的环境中调整之后�Q�MySQL�?PostgreSQL 的执行情况会略有提高�Q�但是SQLite是不需要�Q何优化的�?/font>

The tests found that SQLite is significantly slower than the other databases only on the operations to create an index and to drop a table. However, slowness in these areas will not affect performance on a production database.

�q�个��试发现�Q�SQLite仅仅在执行创建烦引和删除表的操作旉��度要比其他数据库慢得多。然而，�q�些斚w��得低速�ƈ不会影响��C��Z��个生产数据库�?br />

Portability

�U�L��?/font>

Because SQLite databases are stored as single files on the filesystem, they are very portable indeed. A database can be copied from one file to another, even across different operating systems. This means that for a cross-platform distribution you just need to concentrate on making your code portable even when a populated database is to be shipped with the application.

因�ؓSQLite数据库在文�g�pȝ��上是作�ؓ单个文�g存储的，实际上它们是非常�Ҏ��U�L��的。一个数据库可被从一个文件拷贝到另一个文�Ӟ��甚至是跨��不同的操作�pȝ��。这意味着在有一个交叉��^��C��发布的时候，你只需要关注于使你的代�?使其可以�U�L��Q�甚��x��当一个可�U�L��的数据库是和应用一起发布的�?/font>

SQLite has no external dependencies. The SQLite library is self-contained, so the only system requirement to run an application with an embedded SQLite database is the SQLite library itself. Because SQLite can be freely distributed, you can always ensure that this is present.

SQLite没有额外的依赖性。SQLite 库是自持的，因此在运行嵌入式SQLite数据库的时候，仅仅需要的是SQLite的库本��n。因为SQLite能够自由的发布，你��L��可以��保�q�是可行的�?br />

Security
安全

SQLite databases are stored to the filesystem and access control is performed by the underlying operating system based on that file's permission settings.
SQLite 数据库存储在文�g�pȝ��之上�Q�访问控制是由基于操作系�l�之下的的文件权限设定来实现�?/font>�?/p>

Though SQLite can be accessed by processes running as different users if the correct file permissions are set, the database engine does not detect which user is performing a particular operation.

如果正确的文件访问权限设定了�Q�尽��SQLite能够通过�q�程�q�行作�ؓ不同的用��h��被访问，但是数据库引擎�ƈ不检��哪个用��h��在执行一个特别的操作�?/font>

The advantage of this is one of administrative simplicitythere is no need to set up a complex user grants scheme. Any user who has access to read the database file is able to access the database tables and records. Likewise, in a shared environment, users are able to create their own SQLite databases to their file space without any involvement from the system administrators.

它的优点之一��是��理��单，不需要设定复杂的用户授权模式。�Q何拥有访问权利的用户都可以访问数据库表格和记录。同��P��在一个共享环境中�Q�用户可以在他们的自��q��文�g�I�间上创��Z��们自��q��SQLite数据库而不用涉及系�l�管理�?/font>

The disadvantage comes when you want to control permissions at a more finely grained level. There is no GRANT operation that would allow access to particular tables to one set of users but not others. If users have read access, they are able to read the entire database, and if they have write access, you have to be sure of their competence and trustworthiness with the data!
�~�点是，当你需要在更加�l�致�_�度水��^的控制权限的时候，它没有GRANT操作�Q�这个操作允�怸�部分用户可访问特定的表而另一部分用户不行。当用户拥有讉K��许可�Q�他们能够读整个数据库，如果他们有写许可�Q�你必须要确定他们在数据上的的权限和信赖�?/font>�?br />

SQL Implementation

SQL工具

SQLite supports a large subset of the ANSI SQL-92 standard. Some features have a limited implementation and a few features are not supported at all.

SQLite支持ANSI SQL-92标准的大的子集。某些特性有一个有限的工具�Q�其他一些特性�ƈ不都被支持�?/font>
For example, atomic transactions are available but cannot be nested; simple subqueries are possible but correlated subqueries are not; triggers can fire for each row but not for each statement; views are available but are read-only.

例如�Q�原子事务是可用的，但不能嵌套；��单的子查询是可以的，但相互关联的子查询是不行的；触发器可以在每一行触发，但不能在每个语句上触发；视图是可见但是只�ȝ��?br />The list of current limitations is maintained at http://www.sqlite.org/omitted.html with the items at the top of the list indicating which items are most likely to be added to SQLite first.

目前被维护的局限性列表在 http://www.sqlite.org/omitted.html 上，列表的上部的选项指示了哪些选项最有可能被先加入到SQLite
In the vast majority of cases, none of the limitations of SQLite will cause problems when developing your application. For those that you need to work around, the benefits of using a fast, portable embedded database will almost certainly outweigh the cost of the workaround.
在大部分的情况下�Q�SQLite的局限性不会给你的应用开发造成��M��问题。因此，你需要变通的�Ҏ��Q��用一个快速的�Q�可�U�L��的嵌入式数据库的好处��比变通方法的费用好的多�?br />

Customization

定制

The SQLite library includes a very powerful mechanism for adding user-defined functions to the SQL command set. Custom functions can even be written in many of the supported language APIs, not just C/C++.

Additionally, as the SQLite source code is public domain, you are free to examine and modify it as you see fit. If SQLite is missing a feature that you absolutely must have, why not add it yourself and give something back to the community?

此外�Q�因为SQLite的源代码是开攄��Q�你可以自由的检查和修改只要你认为合适。如果SQLite现在�~�少一个你很需要但却还没有的特性，��Z��么不自己��d��然后�l�社区回赠一些呢�Q?/font>

Supported APIs

SQLite now has extensive support for other programming languages through APIs that use the underlying C/C++ interface to communicate with SQLite database files.

C/C++

The core interface is implemented as a single library called libsqlite.so on Linux/Unix systems and sqlite.dll on Windows.

Only the SQLite library is required to allow all users to create their own databases, so very little administration is required to add SQL database capability to a shared system.

PHP

Support for SQLite in PHP has been available for a while, but since the release of PHP 5, it has been shipped with the standard distribution.

Traditionally, PHP and MySQL have gone hand in hand as the interface and back end for dynamic web sites, but it is expected that many more web hosting providers will offer SQLite as PHP 5 gains popularity. From the host's point of view, it is much simpler to administer than a client/server database as there are no complex permissions to manage and database files will be already counted in the disk quota.

Note

SQLite has proved itself to work very well with low- to medium-traffic web sites. As a very rough guideline, if you are expecting over 100,000 hits per dayand in practice, only a small number of web sites will have this level of trafficyou should consider how much database work is done by the web scripts and think about doing some kind of stress testing before committing to SQLite as your back end.

Perl

Perl allows access to SQLite through the Database Interface (DBI) module. This makes it very easy for existing Perl developers to use SQLite within their scripts. The DBI provides an abstraction layer to the Database Driver (DBD), so the same command set is used to access many different types of underlying databases.

The DBD::SQLite driver further allows access to the capabilities of SQLite that the Perl DBI does not allow. Although this does not create a Perl application that can be easily ported to another database back end, it does allow access to the powerful user-defined functions feature.

Tcl

The Tcl interface for SQLite is shipped as part of the SQLite distribution as a library that is imported into Tcl to activate the extensions.

Using Tcl and Tk together with SQLite, you have a platform that is ideal for rapid development of portable graphical user applications.

Other Programming Languages

SQLite has APIs for many other programming languages, including Java, .NET, Smalltalk, and Ruby. As more languages become supported, they are added to the list at http://www.sqlite.org/cvstrac/wiki?p=SqliteWrappers .

Scalability

The downside of using a single file to store databases is that SQLite is not as scalable as many client/server database systems.

The SQLite engine can address database files of up to 2TB in size; however, the restriction on the size of a database is more likely to be enforced by your operating system. In many cases, the size limit on a single file is 2GB.

File locking in SQLite is very coarse-grained. When a write operation takes place, the entire file is locked so that no other process can open it for reading or writing. Larger RDBMSs implement locking at the table or row level so that other processes are able to carry on working unless they are trying to access a specific piece of locked data.

Therefore, if you have a database that is likely to involve massive database files or a high frequency of slow write operations, SQLite may not be suitable and you should consider an RDBMS that is designed and tuned for multiple-user access.

摘自《SQLite�?a class="v1" target="_new">Chris Newman�?/font>

JetSun 2006-05-31 22:25 发表评论

SQLite的介�l?��译)

JetSun — Wed, 31 May 2006 12:40:00 GMT

Introduction

介绍

SQLite is an embeddable SQL-driven database engine that implements both the database engine and its interface as a C/C++ library. Started in 2000 by D. Richard Hipp, it was written from the ground up and contains absolutely no legacy code, and the SQLite source code has been in the public domain since the first prerelease of version 2.0 in 2001.

SQLite是一个嵌入式的SQL驱动的数据库引擎�Q�它可以作�ؓ数据库引擎或者C/C++库的接口使用。它由D. Richard Hipp�?000�q�创建，它是完全重写的绝对不包含��M��的老程序。自�?001�q�的2.0版本SQLite的预发行版发布以来源代码��公开了�?/font>
The primary design goals when SQLite was conceived were that it should be
SQLite构想时候的主要设计目标是：

Simple to administer
易于��理
Simple to operate
易于操作
Simple to use in a program
易于在程序中使用
Simple to maintain and customize
易于�l�护和定�?/font>

The fact that SQLite is small, fast, and reliable arguably its greatest strengthsis, according to Hipp, a happy coincidence. He concentrated on making SQLite simple, and reliability is a byproduct of having fewer things to go wrong. Having simpler code in the database engine makes it much easier to optimize.

按Hipp所��_��事实上SQLite很小�Q�很快和可以信赖的，�q�且证明有卓��的强度�Q�a happy coincidence。他致力于��SQLite��单化�Q�让更少的东西出错的副��品就是可信赖性。数据库引擎代码的简单化使得它的优化�Ҏ��的多�?br />
Note
注意

The acronym SQL is sometimes pronounced sequel, although in common usage it is most often said as three letters. SQLite, however, is pronounced sequel-lite by its creatorin the same way that Microsoft SQL Server is usually pronounced sequel-serverand therefore that is how we have assumed it is said in this book. As we will refer to a SQLite database and an SQL statement, it will help if you are used to hearing them this way as you read on.

首字母所写SQL有时候发音�ؓsequel�Q�虽然在�q�x��使用当中它常常被说成是三个字母。然而，它的发明者的发音�?span class="docEmphasis">sequel-lite�Q�和微��Y的SQL Server通常的发�?sequel-server是一��L��Q�因此本书里面假设是�q�样。当我们谈及SQLite数据库和SQL语句的时候，它将会很有帮助，如果你曾�l�听到过的它们和你阅�ȝ��一栗��?/span>

摘自《SQLite�?/font>Chris Newman�?/font>

JetSun 2006-05-31 20:40 发表评论

JetSun — Wed, 31 May 2006 12:22:00 GMT

Why Use SQLite?

��Z��么��用SQLite�Q?/font>

There are many reasons for choosing SQLite, including
选择SQLite有许多理由，包括�Q?/font>

Performance SQLite performs database operations efficiently and is faster than other free databases such as MySQL and PostgreSQL.
性能 SQLite在执行数据库操作的时候要比诸如MySQL�?/font> PostgreSQL�{�自由数据库高效和快速�?/font>

Size SQLite has a small memory footprint and only a single library is required to access databases, making it ideal for embedded database applications.

大小 SQLite有很��的需要很��的内存�Q��ƈ且访问数据库只需要一个单独的库文�Ӟ��q�些使它成�ؓ嵌入式数据库应用的理想选择�?/font>

Portability SQLite runs on many platforms and its databases can be ported easily with no client/server setup or ongoing administration required.

可移植�?/strong> SQLite可以在很多��^��C��q�行�Q��ƈ且他的数据库可以在没有客��L��/服务器设�|?和管理不间断的情况下�q�行�U�L��?/font>

Stability SQLite is ACID-compliant, meeting all four criteria Atomicity, Consistency, Isolation, and Durability.

�E�_��?/strong> SQLite遵从不可分割性原则，�W�合所有的四个标准原子性，一致性，隔离性，和耐久性�?/font>

SQL support SQLite implements a large subset of the ANSI-92 SQL standard, including views, subqueries, and triggers.

SQL SQLite支持ANSI-92 SQL标准的一个大的子集工��P��包括视图�Q�子查询和触发器�?/font>

Interfaces SQLite has language APIs for C/C++, PHP, Perl, Python, Tcl, and many more beyond those covered in this book.

接口 SQLite�?C/C++, PHP, Perl, Python, Tcl和更多的在本书之外的语言�?/font>

Cost SQLite is in the public domain and therefore is free to use for any purpose without cost and can be freely redistributed.

费用 SQLite 是公开的，因此可以��L��的自�׃��用它而不需要付费，�q�且可以自由的重新发布�?/font>

摘自《SQLite�?a class="v1" target="_new">Chris Newman�?img src ="http://www.shnenglu.com/cc/aggbug/7989.html" width = "1" height = "1" />

JetSun 2006-05-31 20:22 发表评论