SQLite源码剖析(1)

2004

　　声明：本SQLite源码剖析系列为刘兴(http://deepfuture.iyunv.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