SQLite源码剖析(1)

声明：本SQLite源码剖析系列为刘兴(http://deepfuture.iteye.com/)原创，未经笔者授权，任何人和机构不能转载

什么是 sqlite ？

sqlite 是一款轻量级的、基于文件的嵌入式数据库，2000年就已经诞生，经过7年多的发展，直到今天已经成为最流行的嵌入式数据库，包括google在内的公司在其桌面软件中亦使用 sqlite 存储用户数据。由此可以看出，已经没有任何理由去怀疑sqlite的稳定性了。


sqlite的优势？

1. 免配置，和access一样，只要把数据库文件通过ftp上传到服务器上就可以使用，不需要服务器的额外支持

2. 备份方便，因为只是一个文件，只要复制一份该文件，就能备份整个数据库

3. 虽然是轻量级数据库，但他支持最大 2tb 的单个库文件。

4. 快，无与伦比的快。经过实际测试，在几百万记录的情况下，sqlite的插入和查询速度和 mysql 不分上下，快于 sql server，10倍于 access （但这并不意味着它可以替代 sql server ）

 

SQLite源码下载 

    在SQLITE主页上下载源码，选择右边出现以下字样的进行下载

 

 

 

源码分析

我们先分析主程序sqlite3.c

/******************************************************************************

** This file is an amalgamation of many separate C source files from SQLite

** version 3.6.23.1.  By combining all the individual C code files into this

** single large file, the entire code can be compiled as a one translation

** unit.  This allows many compilers to do optimizations that would not be

** possible if the files were compiled separately.  Performance improvements

** of 5% are more are commonly seen when SQLite is compiled as a single

** translation unit.

**

** This file is all you need to compile SQLite.  To use SQLite in other

** programs, you need this file and the "sqlite3.h" header file that defines

** the programming interface to the SQLite library.  (If you do not have

** the "sqlite3.h" header file at hand, you will find a copy embedded within

** the text of this file.  Search for "Begin file sqlite3.h" to find the start

** of the embedded sqlite3.h header file.) Additional code files may be needed

** if you want a wrapper to interface SQLite with your choice of programming

** language. The code for the "sqlite3" command-line shell is also in a

** separate file. This file contains only code for the core SQLite library.

*/

//主程序定义SQLITE核心：define SQLITE_CORE 1

//主程序定义SQLITE_API。

//主程序序版本为合并后的源代码：define SQLITE_AMALGAMATION 1

#define SQLITE_CORE 1

#define SQLITE_AMALGAMATION 1

#ifndef SQLITE_PRIVATE

# define SQLITE_PRIVATE static

#endif

#ifndef SQLITE_API

# define SQLITE_API

#endif

/************** Begin file sqliteInt.h ***************************************/

/*

** 2001 September 15

**

** The author disclaims copyright to this source code.  In place of

** a legal notice, here is a blessing:

**

**    May you do good and not evil.

**    May you find forgiveness for yourself and forgive others.

**    May you share freely, never taking more than you give.

**

*************************************************************************

** Internal interface definitions for SQLite.

**

*/

//SQLITE内部接口定义

#ifndef _SQLITEINT_H_

#define _SQLITEINT_H_

//如果基础操作系统支持，可用#define开启大于2G的单个文件支持。

/*

** These #defines should enable >2GB file support on POSIX if the

** underlying operating system supports it.  If the OS lacks

** large file support, or if the OS is windows, these should be no-ops.

**_LARGEFILE_SOURCE宏必须在任何#include前使用

** Ticket #2739:  The _LARGEFILE_SOURCE macro must appear before any

** system #includes.  Hence, this block of code must be the very first

** code in all source files.

**在编译命令行使用-DSQLITE_DISABLE_LFS可禁止大文件支持，

** Large file support can be disabled using the -DSQLITE_DISABLE_LFS switch

** on the compiler command line.  This is necessary if you are compiling

** on a recent machine (ex: Red Hat 7.2) but you want your code to work

** on an older machine (ex: Red Hat 6.0).  If you compile on Red Hat 7.2

** without this option, LFS is enable.  But LFS does not exist in the kernel

** in Red Hat 6.0, so the code won't work.  Hence, for maximum binary

** portability you should omit LFS.

**

** Similar is true for Mac OS X.  LFS is only supported on Mac OS X 9 and later.

*/

//如果没禁止大文件支持，则定义相关常量

#ifndef SQLITE_DISABLE_LFS

# define _LARGE_FILE       1

# ifndef _FILE_OFFSET_BITS

#   define _FILE_OFFSET_BITS 64

# endif

# define _LARGEFILE_SOURCE 1

#endif

 

/*

** Include the configuration header output by 'configure' if we're using the

** autoconf-based build

*/

//如果使用autoconf-based构建，则include "config.h"

#ifdef _HAVE_SQLITE_CONFIG_H

#include "config.h"

#endif

 

/************** Include sqliteLimit.h in the middle of sqliteInt.h ***********/

/************** Begin file sqliteLimit.h *************************************/

/*

** 2007 May 7

**

** The author disclaims copyright to this source code.  In place of

** a legal notice, here is a blessing:

**

**    May you do good and not evil.

**    May you find forgiveness for yourself and forgive others.

**    May you share freely, never taking more than you give.

**

*************************************************************************

**

** This file defines various limits of what SQLite can process.

*/

 

/*

** The maximum length of a TEXT or BLOB in bytes.   This also

** limits the size of a row in a table or index.

**

** The hard limit is the ability of a 32-bit signed integer

** to count the size: 2^31-1 or 2147483647.

*/

//最大32位有符号整数

#ifndef SQLITE_MAX_LENGTH

# define SQLITE_MAX_LENGTH 1000000000

#endif

 

/*

** This is the maximum number of

**以下这些项的最大值:

**表中的列、索引中的列、视图的列、update的set从句的数量、select

**返回的字段数、GROUP BY 和ORDER BY的字段数、INSERT的values从句

**    * Columns in a table

**    * Columns in an index

**    * Columns in a view

**    * Terms in the SET clause of an UPDATE statement

**    * Terms in the result set of a SELECT statement

**    * Terms in the GROUP BY or ORDER BY clauses of a SELECT statement.

**    * Terms in the VALUES clause of an INSERT statement

**

** The hard upper limit here is 32676.  Most database people will

** tell you that in a well-normalized database, you usually should

** not have more than a dozen or so columns in any table.  And if

** that is the case, there is no point in having more than a few

** dozen values in any of the other situations described above.

*/

/*

**以下这些项的最大值:

**表中的列、索引中的列、视图的列、update的set从句的数量、select

**返回的字段数、GROUP BY 和ORDER BY的字段数、INSERT的values从句

*/

#ifndef SQLITE_MAX_COLUMN

# define SQLITE_MAX_COLUMN 2000

#endif

 

/*

** The maximum length of a single SQL statement in bytes.

**

** It used to be the case that setting this value to zero would

** turn the limit off.  That is no longer true.  It is not possible

** to turn this limit off.

*/

//SQL语句的最大长度

#ifndef SQLITE_MAX_SQL_LENGTH

# define SQLITE_MAX_SQL_LENGTH 1000000000

#endif

 

/*

** The maximum depth of an expression tree. This is limited to

** some extent by SQLITE_MAX_SQL_LENGTH. But sometime you might

** want to place more severe limits on the complexity of an

** expression.

**

** A value of 0 used to mean that the limit was not enforced.

** But that is no longer true.  The limit is now strictly enforced

** at all times.

*/

//解释树的最大深度

#ifndef SQLITE_MAX_EXPR_DEPTH

# define SQLITE_MAX_EXPR_DEPTH 1000

#endif

 

/*

** The maximum number of terms in a compound SELECT statement.

** The code generator for compound SELECT statements does one

** level of recursion for each term.  A stack overflow can result

** if the number of terms is too large.  In practice, most SQL

** never has more than 3 or 4 terms.  Use a value of 0 to disable

** any limit on the number of terms in a compount SELECT.

*/

//复合SQL语句的最大项数

#ifndef SQLITE_MAX_COMPOUND_SELECT

# define SQLITE_MAX_COMPOUND_SELECT 500

#endif