SQLite

<h1 align="center">SQLite Source Repository</h1>

This repository contains the complete source code for the SQLite database
engine.  Some test scripts are also include.  However, many other test scripts
and most of the documentation are managed separately.

## Compiling

First create a directory in which to place
the build products.  It is recommended, but not required, that the
build directory be separate from the source directory.  Cd into the
build directory and then from the build directory run the configure
script found at the root of the source tree.  Then run "make".

For example:

    tar xzf sqlite.tar.gz    ;#  Unpack the source tree into "sqlite"
    mkdir bld                ;#  Build will occur in a sibling directory
    cd bld                   ;#  Change to the build directory
    ../sqlite/configure      ;#  Run the configure script
    make                     ;#  Run the makefile.
    make sqlite3.c           ;#  Build the "amalgamation" source file
    make test                ;#  Run some tests (requires TCL)

See the makefile for additional targets.

The configure script uses autoconf 2.61 and libtool.  If the configure
script does not work out for you, there is a generic makefile named
"Makefile.linux-gcc" in the top directory of the source tree that you
can copy and edit to suit your needs.  Comments on the generic makefile
show what changes are needed.







SQLite does not require TCL to run, but a TCL installation is required
by the makefiles.  SQLite contains a lot of generated code and TCL is
used to do much of that code generation.  The makefile also requires
AWK.

## Source Code Tour

Most of the core source files are in the **src/** subdirectory.  But
src/ also contains files used to build the "testfixture" test harness;
those file all begin with "test".  And src/ contains the "shell.c" file
which is the main program for the "sqlite3.exe" command-line shell and
the "tclsqlite.c" file which implements the bindings to SQLite from the
TCL programming language.  (Historical note:  SQLite began as a TCL
extension and only later escaped to the wild as an independent library.)

Test scripts and programs are found in the **test/** subdirectory.
There are other test suites for SQLite (see 
[How SQLite Is Tested](http://www.sqlite.org/testing.html))
but those other test suites are
in separate source repositories.

The **ext/** subdirectory contains code for extensions.  The
Full-text search engine is in **ext/fts3**.  The R-Tree engine is in
**ext/rtree**.  The **ext/misc** subdirectory contains a number of
smaller, single-file extensions, such as a REGEXP operator.

The **tool/** subdirectory contains various scripts and programs used
for building generated source code files or for testing or for generating
accessory programs such as "sqlite3_analyzer(.exe)".

### Generated Source Code Files

Several of the C-language source files used by SQLite are generated from
other sources rather than being typed in manually by a programmer.  This
section will summarize those automatically-generated files.  To create all
of the automatically-generated files, simply run "make target&#95;source".
The "target&#95;source" make target will create a subdirectory "tsrc/" and
fill it with all the source files needed to build SQLite, both 
manually-edited files and automatically-generated files.

The SQLite interface is defined by the **sqlite3.h** header file, which is
generated from src/sqlite.h.in, ./manifest.uuid, and ./VERSION.  The
TCL script at tool/mksqlite3h.tcl does the conversion.  The manifest.uuid
file contains the SHA1 hash of the particular check-in and is used to generate
the SQLITE_SOURCE_ID macro.  The VERSION file contains the current SQLite
version number.  The sqlite3.h header is really just a copy of src/sqlite.h.in
with the source-id and version number inserted at just the right spots.
Note that comment text in the sqlite3.h file is used to generate much of
the SQLite API documentation.  The TCL scripts used to generate that
documentation are in a separate source repository.

The SQL language parser is **parse.c** which is generate from a grammar in
the src/parse.y file.  The conversion of "parse.y" into "parse.c" is done
by the [lemon](./doc/lemon.html) LALR(1) parser generator.  The source code 
for lemon is at tool/lemon.c.  Lemon uses a
template for generating its parser.  A generic template is in tool/lempar.c,
but SQLite uses a slightly modified template found in src/lempar.c.

Lemon also generates the **parse.h** header file, at the same time it
generates parse.c. But the parse.h header file is
modified further (to add additional symbols) using the ./addopcodes.awk
AWK script.

The **opcodes.h** header file contains macros that define the numbers
corresponding to opcodes in the "VDBE" virtual machine.  The opcodes.h
file is generated by the scanning the src/vdbe.c source file.  The
AWK script at ./mkopcodeh.awk does this scan and generates opcodes.h.
A second AWK script, ./mkopcodec.awk, then scans opcodes.h to generate
the **opcodes.c** source file, which contains a reverse mapping from
opcode-number to opcode-name that is used for EXPLAIN output.

The **keywordhash.h** header file contains the definition of a hash table
that maps SQL language keywords (ex: "CREATE", "SELECT", "INDEX", etc.) into
the numeric codes used by the parse.c parser.  The keywordhash.h file is
generated by a C-language program at tool mkkeywordhash.c.

### The Amalgamation

All of the individual C source code and header files (both manually-edited
and automatically-generated) can be combined into a single big source file
**sqlite3.c** called "the amalgamation".  The amalgamation is the recommended
way of using SQLite in a larger application.  Combining all individual
source code files into a single big source code file allows the C compiler
to perform more cross-procedure analysis and generate better code.  SQLite
runs about 5% faster when compiled from the amalgamation versus when compiled
from individual source files.

The amalgamation is generated from the tool/mksqlite3c.tcl TCL script.
First, all of the individual source files must be gathered into the tsrc/
subdirectory (using the equivalent of "make target_source") then the
tool/mksqlite3c.tcl script is run to copy them all together in just the
right order while resolving internal "#include" references.

The amalgamation source file is more than 100K lines long.  Some symbolic
debuggers (most notably MSVC) are unable to deal with files longer than 64K
lines.  To work around this, a separate TCL script, tool/split-sqlite3c.tcl,
can be run on the amalgamation to break it up into a single small C file
called **sqlite3-all.c** that does #include on about five other files
named **sqlite3-1.c**, **sqlite3-2.c**, ..., **sqlite3-5.c**.  In this way,
all of the source code is contained within a single translation unit so
that the compiler can do extra cross-procedure optimization, but no 
individual source file exceeds 32K lines in length.

## How It All Fits Together

SQLite is modular in design.
See the [architectural description](http://www.sqlite.org/arch.html) 
for details. Other documents that are useful in
(helping to understand how SQLite works include the
[file format](http://www.sqlite.org/fileformat2.html) description,
the [virtual machine](http://www.sqlite.org/vdbe.html) that runs
prepared statements, the description of 
[how transactions work](http://www.sqlite.org/atomiccommit.html), and
the [overview of the query planner](http://www.sqlite.org/optoverview.html).

Unfortunately, years of effort have gone into optimizating SQLite, both
for small size and high performance.  And optimizations tend to result in
complex code.  So there is a lot of complexity in the SQLite implementation.

Key files:

  *  **sqlite3.h** - This file defines the public interface to the SQLite
     library.  Readers will need to be familiar with this interface before
     trying to understand how the library works internally.

  *  **sqliteInt.h** - this header file defines many of the data objects
     used internally by SQLite.

  *  **parse.y** - This file describes the LALR(1) grammer that SQLite uses
     to parse SQL statements, and the actions that are taken at each stop
     in the parsing process.

  *  **vdbe.c** - This file implements the virtual machine that runs
     prepared statements.  There are various helper files whose names
     begin with "vdbe".  The VDBE has access to the vdbeInt.h header file
     which defines internal data objects.  The rest of SQLite interacts
     with the VDBE through an interface defined by vdbe.h.

  *  **where.c** - This file analyzes the WHERE clause and generates
     virtual machine code to run queries efficiently.  This file is
     sometimes called the "query optimizer".  It has its own private
     header file, whereInt.h, that defines data objects used internally.

  *  **btree.c** - This file contains the implementation of the B-Tree
     storage engine used by SQLite.

  *  **pager.c** - This file contains the "pager" implementation, the
     module that implements transactions.

  *  **os_unix.c** and **os_win.c** - These two files implement the interface
     between SQLite and the underlying operating system using the run-time
     pluggable VFS interface.
  

## Contacts

The main SQLite webpage is [http://www.sqlite.org/](http://www.sqlite.org/)
with geographically distributed backup servers at
[http://www2.sqlite.org/](http://www2.sqlite.org) and
[http://www3.sqlite.org/](http://www3.sqlite.org).