Documentation Source Text

<title>File Format For SQLite Databases</title>
<tcl>hd_keywords {file format} {second edition file format document}</tcl>

<h1 align=center>
The SQLite Database File Format
</h1>

<p>This document describes and defines the on-disk database file
format used by SQLite.</p>

<h2>1.0 The Database File</h2>

<p>The complete state of an SQLite database is usually
contained a single file on disk called the "main database file".</p>

<p>While performing a transaction, the default behavior is to stores 
some temporary information in a second file called the "rollback journal".
(The alternative is to use a [write-ahead log] - described separately.)
If the application or
host computer crashes before completing the transaction, then the rollback
journal contains critical state information needed to restore the

</ol>

<p>^New database files created by SQLite use format 1 by default, so
that database files created by newer versions of SQLite can still
be read by older versions of SQLite.
^The [legacy_file_format pragma] can be used to cause SQLite
to create new database files using format 4.  Future versions of 
SQLite may begin to create files using format 4 by default.
The format version number can be made to default to 4 instead of 1 by
setting [SQLITE_DEFAULT_FILE_FORMAT]=4 at compile-time.
</p>

<h4>1.2.11 Suggested cache size</h4>

<p>The 4-byte big-endian signed integer at offset 48 is the suggested
cache size in pages for the database file.  The value is a suggestion
only and SQLite is under no obligation to honor it.  The absolute value
of the integer is used as the suggested size.  The suggested cache size
can be set using the [default_cache_size pragma].</p>

<h4>1.2.12 Incremental vacuum settings</h4>

to either truncate or zero the header of the wal-index when the last
connection to it closes.  Because the wal-index is transient, it can
use an architecture-specific format; it does not have to be cross-platform.
Hence, unlike the database and WAL file formats which store all values
as big endian, the wal-index stores multi-byte values in the native
byte order of the host computer.</p>

<p>This document is concerned with the persistent state of the database
file, and since the wal-index is a transient structure, no further 
information about the format of the wal-index will be provided here.
Complete details on the format of the wal-index are contained within
comments in SQLite source code.</p>