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<th colspan="3" align="center">Changed PRAGMAs</th>
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<td width="20%" align="left"><a accesskey="p" href="unsupportedpragmas.html">Prev</a> </td>
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<div class="sect1" lang="en" xml:lang="en">
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<div>
<h2 class="title" style="clear: both"><a id="changedpragmas"></a>Changed PRAGMAs</h2>
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<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="changedpragmas.html#auto_vacuum">PRAGMA auto_vacuum</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="changedpragmas.html#incremental_vacuum">PRAGMA incremental_vacuum</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="changedpragmas.html#journal_size_limit">PRAGMA journal_size_limit</a>
</span>
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<p>
The following PRAGMAs are available in the BDB SQL interface, but they
behave differently in some way from standard SQLite.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="auto_vacuum"></a>PRAGMA auto_vacuum</h3>
</div>
</div>
</div>
<p>
The syntax for this PRAGMA is:
</p>
<pre class="programlisting">PRAGMA auto_vacuum
PRAGMA auto_vacuum = 0 | NONE | 1 | FULL | 2 | INCREMENTAL </pre>
<p>
Standard SQLite does not allow you to enable or
disable auto-vacuum after a table has been created.
Berkeley DB, however, allows you to change this at any time.
</p>
<p>
In the previous syntax, <code class="literal">0</code> and
<code class="literal">NONE</code> both turn off auto vacuuming.
</p>
<p>
<code class="literal">1</code> or <code class="literal">FULL</code> causes
full vacuuming to occur. That is, the BDB SQL interface will vacuum
the entire database at each commit using a very low
fill percentage (1%) in order to return emptied pages
to the file system. Because Berkeley DB allows you to call
this PRAGMA at any time, it is recommended that you do
not turn on FULL vacuuming because doing so can result
in a great deal of overhead to your transaction
commits.
</p>
<p>
If <code class="literal">2</code> or <code class="literal">INCREMENTAL</code>
is used, then incremental vacuuming is enabled. The
amount of vacuuming that is performed for incremental
vacuum is controlled using the following PRAGMAs:
</p>
<table class="simplelist" border="0" summary="Simple list">
<tr>
<td>
<a class="xref" href="addedpragmas.html#bdbsql_vacuum_fillpercent" title="PRAGMA bdbsql_vacuum_fillpercent">PRAGMA bdbsql_vacuum_fillpercent</a>
</td>
</tr>
<tr>
<td>
<a class="xref" href="addedpragmas.html#bdbsql_vacuum_pages" title="PRAGMA bdbsql_vacuum_pages">PRAGMA bdbsql_vacuum_pages</a>
</td>
</tr>
</table>
<p>
Note that you can call
<a class="xref" href="changedpragmas.html#incremental_vacuum" title="PRAGMA incremental_vacuum">PRAGMA incremental_vacuum</a>
to perform an incremental vacuum operation on demand.
</p>
<p>
When performing vacuum operations, Berkeley DB
defragments and repacks individual database pages,
while SQLite only truncates the freelist pages from
the database file.
</p>
<p>
For more information on auto vacuum, see
<a class="ulink" href="http://www.sqlite.org/pragma.html#pragma_auto_vacuum" target="_top">PRAGMA auto_vacuum</a>
in the SQLite documentation.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="incremental_vacuum"></a>PRAGMA incremental_vacuum</h3>
</div>
</div>
</div>
<p>
Performs incremental vacuum operations on demand. You can cause
incremental vacuum operations to be performed automatically using
<a class="xref" href="changedpragmas.html#auto_vacuum" title="PRAGMA auto_vacuum">PRAGMA auto_vacuum</a>.
</p>
<p>
Note that for SQLite, this PRAGMA is used to specify
the maximum number of pages to be freed during
vacuuming. For Berkeley DB, you use
<code class="literal">PRAGMA bdbsql_vacuum_pages</code> instead.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="journal_size_limit"></a>PRAGMA journal_size_limit</h3>
</div>
</div>
</div>
<p>
For standard SQLite, this pragma identifies the
maximum size that the journal file is allowed to be.
</p>
<p>
Berkeley DB uses multiple journal files, Berkeley DB journal
files are different to a SQLite journal file in that they
contain information about multiple transactions, rather
than a single transaction (similar to the SQLite WAL
journal file). Over the course
of the database's lifetime, Berkeley DB will probably create
multiple journal files. A new journal file is created when
the current journal file has reached the maximum size
configured using the journal_size_limit pragma.
</p>
<p>
Note that a BDB SQL interface journal file is referred to as a log
file in the Berkeley DB documentation.
</p>
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