Documentation Source Text

<title>SQLite Features</title>

<h2>About SQLite</h2>

<h3>SQLite Features:</h3>

<p><ul>
<li><a href="transactional.html">Transactions</a>
    are atomic, consistent, isolated, and durable (ACID)

<p><ul>
<li><p><b>Application File Format.</b>
Rather than using fopen() to write XML or some proprietary format into
disk files used by your application, use an SQLite database instead.
You'll avoid having to write and troubleshoot a parser, your data
will be more easily accessible and cross-platform, your updates
will be transactional.</p></li>

<li><p><b>Database For Gadgets.</b>
SQLite is popular choice for the database engine in cellphones,
PDAs, MP3 players, set-top boxes, and other electronic gadgets.
SQLite has a small code footprint, makes efficient use of memory,
disk space, and disk bandwidth, is highly reliable, and requires
no maintenance from a Database Adminstrator.</p></li>

Let us use that number as a proxy for the number of deployed
SQL database engines other than SQLite.  Not every website
runs an SQL database engine, and not ever SQL database engine
runs a website.  Larger websites run multiple
database engines.  But the vast majority of smaller websites
(the long tail) share
a database engine with several other websites,
if they use a database engine at all.
And many large SQL database installations have nothing to do with
websites.
So using the number of websites as a surrogate for the number of operational
SQL database engines is a crude approximation, but it is the best
we have so we will go with it.  (Readers are encouraged to submit
better estimates.)</p>

<title>SQLite: Single File Database</title>

<h2>Single-file Cross-platform Database</h2>

<p>
A database in SQLite is a single disk file.
Furthermore, the file format is cross-platform.
A database that is created on one machine can be
copied and used on a different machine with
a different architecture.  SQLite databases
are portable across 32-bit and 64-bit machines
and between 
<a href="http://en.wikipedia.org/wiki/Endianness">big-endian</a> and 
<a href="http://en.wikipedia.org/wiki/Endianness">little-endian</a>
architectures.

"amalgamation" - a single large C source code file.
Projects that want to include SQLite can do so simply
by dropping this one source file (named "sqlite3.c") and
its corresponding header ("sqlite3.h") into their source
tree and compiling it together with the rest of the
code.  SQLite does not link against any external libraries
(other than the C library, as described above) and does
not require any special build support.
</p>

<title>SQLite Is Serverless</title>

<h2>SQLite Is Serverless</h2>

<p>
Most SQL database engines are implemented as a separate server process.
Programs that want to access the database communicate with the server
using some kind of interprocess communication (typically TCP/IP) to send 
requests to the server and to receive back results. 
SQLite does not work this way. 
With SQLite, the process that wants to access the database reads and 
writes directly from the database files on disk. 
There is no intermediary server process.
</p>

And because a server is a single persistent process,
it is able control database access with more precision, 
allowing for finer grain locking and better concurrancy.
</p>

<p>
Most SQL database engines are client/server based. 
Of those that are serverless, SQLite is the only one
known to this author that allows multiple applications
to access the same database at the same time. 
</p>