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<h2 class="title" style="clear: both"><a id="dbclose"></a>Db::close()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
Db::close(u_int32_t flags);</pre>
<p>
The <code class="methodname">Db::close()</code> method flushes any cached database information to
disk, closes any open cursors, frees any allocated resources, and
closes any underlying files.
</p>
<p>
Although closing a database handle will close any open cursors, it
is recommended that applications explicitly close all their
<a class="link" href="dbc.html" title="Chapter 3. The Dbc Handle">Dbc</a> handles
before closing the database. The reason why is that when
the cursor is explicitly closed, the memory allocated for it is
reclaimed; however, this will <span class="emphasis"><em>not</em></span> happen if
you close a database while cursors are still opened.
</p>
<p>
The same rule, for the same reasons, hold true for
<a class="link" href="txn.html" title="Chapter 13. The DbTxn Handle">DbTxn</a>
handles. Simply make sure you close all your transaction handles
before closing your database handle.
</p>
<p>
Because key/data pairs are cached in memory, applications should
make a point to always either close database handles or sync their
data to disk (using the <a class="xref" href="dbsync.html" title="Db::sync()">Db::sync()</a>
method) before exiting, to ensure that any data cached in main memory are
reflected in the underlying file system.
</p>
<p>
When called on a database that is the primary database for a secondary
index, the primary database should be closed only after all secondary
indices referencing it have been closed.
</p>
<p>
When multiple threads are using the <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a>
concurrently, only a single thread may call the <code class="methodname">Db::close()</code> method.
</p>
<p>
The <a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a> handle may not be
accessed again after <code class="methodname">Db::close()</code> is called, regardless of its return.
</p>
<p>
The <code class="methodname">Db::close()</code> <span>
<span>
method either returns a non-zero error value or throws an
exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</span>
</span>
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1630391"></a>Parameters</h3>
</div>
</div>
</div>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1631913"></a>flags</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>flags</strong></span> parameter must be set to 0
or be set to the following value:
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p><a id="dbclose_DB_NOSYNC"></a>
<code class="literal">DB_NOSYNC</code>
</p>
<p>
Do not flush cached information to disk. This flag is a
dangerous option. It should be set only if the application is doing
logging (with transactions) so that the database is recoverable after
a system or application crash, or if the database is always generated
from scratch after any system or application crash.
</p>
<p>
<span class="bold"><strong>It is important to understand that flushing
cached information to disk only minimizes the window of opportunity
for corrupted data.</strong></span> Although unlikely, it is possible for
database corruption to happen if a system or application crash occurs
while writing data to the database. To ensure that database
corruption never occurs, applications must either: use transactions
and logging with automatic recovery; use logging and
application-specific recovery; or edit a copy of the database, and
once all applications using the database have successfully called
<code class="methodname">Db::close()</code>, atomically replace the original database with the
updated copy.
</p>
<p>
Note that this flag only works when the database
has been opened using an environment.
</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1631752"></a>Errors</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">Db::close()</code> <span>
<span>
method may fail and throw a <a class="link" href="dbexception.html" title="Chapter 6. The DbException Class">DbException</a>
exception, encapsulating one of the following non-zero errors, or return one
of the following non-zero errors:
</span>
</span>
</p>
<div class="sect3" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id1629775"></a>EINVAL</h4>
</div>
</div>
</div>
<p>
An invalid flag value or parameter was specified.
</p>
</div>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1631932"></a>Class</h3>
</div>
</div>
</div>
<p>
<a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a>
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1631791"></a>See Also</h3>
</div>
</div>
</div>
<p>
<a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a>
</p>
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