<title>File Format Changes in SQLite</title>

<h2>File Format Changes in SQLite</h2>

<p>
The [file format|underlying file format] for SQLite databases does not
change in incompatible ways.  There are literally hundreds of billions,
perhaps trillions, of
SQLite database files in circulation and the SQLite developers are
committing to supporting those files for decades into the future.
</p>

<p>
This document describes incompatibilities that have occurred in
SQLite prior to 2004.  Since 2004, there have been enhancements to
SQLite such that newer database files are unreadable by older versions
of the SQLite library.  But the most recent versions of the SQLite
library should be able to read and write any older SQLite database
file without any problems.
</p>

<p>
In other words, since 2004 all SQLite releases have been backwards
compatible, though not necessarily forwards compatible.
</p>

<p>
The following table summarizes the SQLite file format changes that have
occurred since version 1.0.0:
</p>

<blockquote>
<table border=2 cellpadding=5>
<tr>
  <th>Version Change</th>
  <th>Approx. Date</th>
  <th>Description Of File Format Change</th>
</tr>
<tr>
  <td valign="top">1.0.32 to 2.0.0</td>
  <td valign="top">2001-09-20</td>
  <td>Version 1.0.X of SQLite used the GDBM library as its backend
  interface to the disk.  Beginning in version 2.0.0, GDBM was replaced
  by a custom B-Tree library written especially for SQLite.  The new
  B-Tree backend is twice as fast as GDBM, supports atomic commits and
  rollback, and stores an entire database in a single disk file instead
  using a separate file for each table as GDBM does.  The two
  file formats are not even remotely similar.</td>
</tr>
<tr>
  <td valign="top">2.0.8 to 2.1.0</td>
  <td valign="top">2001-10-12</td>
  <td>The same basic B-Tree format is used but the details of the 
  index keys were changed in order to provide better query 
  optimization opportunities.  Some of the headers were also changed in order
  to increase the maximum size of a row from 64KB to 24MB.<p>

  This change is an exception to the version number rule described above
  in that it is neither forwards or backwards compatible.  A complete
  reload of the database is required.  This is the only exception.</td>
</tr>
<tr>
  <td valign="top">2.1.7 to 2.2.0</td>
  <td valign="top">2001-12-21</td>
  <td>Beginning with version 2.2.0, SQLite no longer builds an index for
  an INTEGER PRIMARY KEY column.  Instead, it uses that column as the actual
  B-Tree key for the main table.<p>Version 2.2.0 and later of the library
  will automatically detect when it is reading a 2.1.x database and will
  disable the new INTEGER PRIMARY KEY feature.   In other words, version
  2.2.x is backwards compatible to version 2.1.x.  But version 2.1.x is not
  forward compatible with version 2.2.x. If you try to open
  a 2.2.x database with an older 2.1.x library and that database contains
  an INTEGER PRIMARY KEY, you will likely get a coredump.  If the database
  schema does not contain any INTEGER PRIMARY KEYs, then the version 2.1.x
  and version 2.2.x database files will be identical and completely
  interchangeable.</p>
</tr>
<tr>
  <td valign="top">2.2.5 to 2.3.0</td>
  <td valign="top">2002-01-30</td>
  <td>Beginning with version 2.3.0, SQLite supports some additional syntax
  (the "ON CONFLICT" clause) in the CREATE TABLE and CREATE INDEX statements
  that are stored in the SQLITE_MASTER table.  If you create a database that
  contains this new syntax, then try to read that database using version 2.2.5
  or earlier, the parser will not understand the new syntax and you will get
  an error.  Otherwise, databases for 2.2.x and 2.3.x are interchangeable.</td>
</tr>
<tr>
  <td valign="top">2.3.3 to 2.4.0</td>
  <td valign="top">2002-03-10</td>
  <td>Beginning with version 2.4.0, SQLite added support for views. 
  Information about views is stored in the SQLITE_MASTER table.  If an older
  version of SQLite attempts to read a database that contains VIEW information
  in the SQLITE_MASTER table, the parser will not understand the new syntax
  and initialization will fail.  Also, the
  way SQLite keeps track of unused disk blocks in the database file
  changed slightly.
  If an older version of SQLite attempts to write a database that
  was previously written by version 2.4.0 or later, then it may leak disk
  blocks.</td>
</tr>
<tr>
  <td valign="top">2.4.12 to 2.5.0</td>
  <td valign="top">2002-06-17</td>
  <td>Beginning with version 2.5.0, SQLite added support for triggers. 
  Information about triggers is stored in the SQLITE_MASTER table.  If an older
  version of SQLite attempts to read a database that contains a CREATE TRIGGER
  in the SQLITE_MASTER table, the parser will not understand the new syntax
  and initialization will fail.
  </td>
</tr>
<tr>
  <td valign="top">2.5.6 to 2.6.0</td>
  <td valign="top">2002-07-17</td>
  <td>A design flaw in the layout of indices required a file format change
  to correct.  This change appeared in version 2.6.0.<p>

  If you use version 2.6.0 or later of the library to open a database file
  that was originally created by version 2.5.6 or earlier, an attempt to
  rebuild the database into the new format will occur automatically.
  This can take some time for a large database.  (Allow 1 or 2 seconds
  per megabyte of database under Unix - longer under Windows.)  This format
  conversion is irreversible.  It is <strong>strongly</strong> suggested
  that you make a backup copy of older database files prior to opening them
  with version 2.6.0 or later of the library, in case there are errors in
  the format conversion logic.<p>

  Version 2.6.0 or later of the library cannot open read-only database
  files from version 2.5.6 or earlier, since read-only files cannot be
  upgraded to the new format.</p>
  </td>
</tr>
<tr>
  <td valign="top">2.6.3 to 2.7.0</td>
  <td valign="top">2002-08-13</td>
  <td><p>Beginning with version 2.7.0, SQLite understands two different
  datatypes: text and numeric.  Text data sorts in memcmp() order.
  Numeric data sorts in numerical order if it looks like a number,
  or in memcmp() order if it does not.</p>

  <p>When SQLite version 2.7.0 or later opens a 2.6.3 or earlier database,
  it assumes all columns of all tables have type "numeric".  For 2.7.0
  and later databases, columns have type "text" if their datatype
  string contains the substrings "char" or "clob" or "blob" or "text".
  Otherwise they are of type "numeric".</p>

  <p>Because "text" columns have a different sort order from numeric,
  indices on "text" columns occur in a different order for version
  2.7.0 and later database.  Hence version 2.6.3 and earlier of SQLite 
  will be unable to read a 2.7.0 or later database.  But version 2.7.0
  and later of SQLite will read earlier databases.</p>
  </td>
</tr>
<tr>
  <td valign="top">2.7.6 to 2.8.0</td>
  <td valign="top">2003-02-14</td>
  <td><p>Version 2.8.0 introduces a change to the format of the rollback
  journal file.  The main database file format is unchanged.  Versions
  2.7.6 and earlier can read and write 2.8.0 databases and vice versa.
  Version 2.8.0 can rollback a transaction that was started by version
  2.7.6 and earlier.  But version 2.7.6 and earlier cannot rollback a
  transaction started by version 2.8.0 or later.</p>

  <p>The only time this would ever be an issue is when you have a program
  using version 2.8.0 or later that crashes with an incomplete
  transaction, then you try to examine the database using version 2.7.6 or
  earlier.  The 2.7.6 code will not be able to read the journal file
  and thus will not be able to rollback the incomplete transaction
  to restore the database.</p>
  </td>
</tr>
<tr>
  <td valign="top">2.8.14 to 3.0.0</td>
  <td valign="top">2004-06-18</td>
  <td><p>Version 3.0.0 is a major upgrade for SQLite that incorporates
  support for UTF-16, BLOBs, and a more compact encoding that results
  in database files that are typically 25% to 50% smaller.  The new file
  format is very different and is completely incompatible with the
  version 2 file format.</p>
  </td>
</tr>
</table>
</blockquote>
