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<!--$Id: db_close.so,v 10.27 2000/09/08 15:20:28 bostic Exp $-->
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<title>Berkeley DB: Db::close</title>
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<h1>Db::close</h1>
</td>
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<h3><pre>
#include &lt;db_cxx.h&gt;
<p>
int
Db::close(u_int32_t flags);
</pre></h3>
<h1>Description</h1>
<p>The Db::close method flushes any cached database information to disk,
closes any open cursors, frees any allocated resources, and closes any
underlying files. Since key/data pairs are cached in memory, failing to
sync the file with the Db::close or <a href="../api_cxx/db_sync.html">Db::sync</a> method may result
in inconsistent or lost information.
<p>The <b>flags</b> parameter must be set to 0 or the following value:
<p><dl compact>
<p><dt><a name="DB_NOSYNC">DB_NOSYNC</a><dd>Do not flush cached information to disk.
<p>The <a href="../api_cxx/db_close.html#DB_NOSYNC">DB_NOSYNC</a> flag is a dangerous option. It should only be set
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><b>It is important to understand that flushing cached information to disk
only minimizes the window of opportunity for corrupted data.</b>
While 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
Db::close, atomically replace the original database with the
updated copy.
</dl>
<p>When multiple threads are using the Berkeley DB handle concurrently, only a single
thread may call the Db::close method.
<p>Once Db::close has been called, regardless of its return, the
<a href="../api_cxx/db_class.html">Db</a> handle may not be accessed again.
<a name="3"><!--meow--></a>
<p>The Db::close method either returns a non-zero error value or throws an exception that
encapsulates a non-zero error value on failure, 0 on success, and returns <a href="../api_c/memp_fsync.html#DB_INCOMPLETE">DB_INCOMPLETE</a> if the underlying database still has
dirty pages in the cache. (The only reason to return
<a href="../api_c/memp_fsync.html#DB_INCOMPLETE">DB_INCOMPLETE</a> is if another thread of control was writing pages
in the underlying database file at the same time as the
Db::close method was called. For this reason, a return of
<a href="../api_c/memp_fsync.html#DB_INCOMPLETE">DB_INCOMPLETE</a> can normally be ignored, or, in cases where it is
a possible return value, the <a href="../api_cxx/db_close.html#DB_NOSYNC">DB_NOSYNC</a> option should probably
have been specified.)
<p>The Db::close 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.
<h1>Errors</h1>
<p>The Db::close method may fail and throw an exception or return a non-zero error for errors specified for other Berkeley DB and C library or system methods.
If a catastrophic error has occurred, the Db::close method may fail and either
return <a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a> or throw an exception encapsulating
<a href="../ref/program/errorret.html#DB_RUNRECOVERY">DB_RUNRECOVERY</a>, in which case all subsequent Berkeley DB calls will fail
in the same way.
<h3>Class</h3>
<a href="../api_cxx/db_class.html">Db</a>
<h1>See Also</h1>
<a href="../api_cxx/db_close.html">Db::close</a>,
<a href="../api_cxx/db_cursor.html">Db::cursor</a>,
<a href="../api_cxx/db_del.html">Db::del</a>,
<a href="../api_cxx/db_err.html">Db::err</a>,
<a href="../api_cxx/db_fd.html">Db::fd</a>,
<a href="../api_cxx/db_get.html">Db::get</a>,
<a href="../api_cxx/db_get_byteswapped.html">Db::get_byteswapped</a>,
<a href="../api_cxx/db_get_type.html">Db::get_type</a>,
<a href="../api_cxx/db_join.html">Db::join</a>,
<a href="../api_cxx/db_key_range.html">Db::key_range</a>,
<a href="../api_cxx/db_open.html">Db::open</a>,
<a href="../api_cxx/db_put.html">Db::put</a>,
<a href="../api_cxx/db_remove.html">Db::remove</a>,
<a href="../api_cxx/db_set_bt_compare.html">Db::set_bt_compare</a>,
<a href="../api_cxx/db_set_bt_minkey.html">Db::set_bt_minkey</a>,
<a href="../api_cxx/db_set_bt_prefix.html">Db::set_bt_prefix</a>,
<a href="../api_cxx/db_set_cachesize.html">Db::set_cachesize</a>,
<a href="../api_cxx/db_set_dup_compare.html">Db::set_dup_compare</a>,
<a href="../api_cxx/db_set_errcall.html">Db::set_errcall</a>,
<a href="../api_cxx/db_set_errfile.html">Db::set_errfile</a>,
<a href="../api_cxx/db_set_errpfx.html">Db::set_errpfx</a>,
<a href="../api_cxx/db_set_flags.html">Db::set_flags</a>,
<a href="../api_cxx/db_set_h_ffactor.html">Db::set_h_ffactor</a>,
<a href="../api_cxx/db_set_h_hash.html">Db::set_h_hash</a>,
<a href="../api_cxx/db_set_h_nelem.html">Db::set_h_nelem</a>,
<a href="../api_cxx/db_set_lorder.html">Db::set_lorder</a>,
<a href="../api_cxx/db_set_malloc.html">Db::set_malloc</a>,
<a href="../api_cxx/db_set_pagesize.html">Db::set_pagesize</a>,
<a href="../api_cxx/db_set_paniccall.html">Db::set_paniccall</a>,
<a href="../api_cxx/db_set_q_extentsize.html">Db::set_q_extentsize</a>,
<a href="../api_cxx/db_set_realloc.html">Db::set_realloc</a>,
<a href="../api_cxx/db_set_re_delim.html">Db::set_re_delim</a>,
<a href="../api_cxx/db_set_re_len.html">Db::set_re_len</a>,
<a href="../api_cxx/db_set_re_pad.html">Db::set_re_pad</a>,
<a href="../api_cxx/db_set_re_source.html">Db::set_re_source</a>,
<a href="../api_cxx/db_stat.html">Db::stat</a>,
<a href="../api_cxx/db_sync.html">Db::sync</a>,
<a href="../api_cxx/db_upgrade.html">Db::upgrade</a>
and
<a href="../api_cxx/db_verify.html">Db::verify</a>.
</tt>
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