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 ）
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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
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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
