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<h2 class="title">Requirements</h2>
<p class="para">
The behaviour of various aspects depends on the implementation of the
underlying database. Functions such as <span class="function"><a href="function.dba-optimize.html" class="function">dba_optimize()</a></span>
and <span class="function"><a href="function.dba-sync.html" class="function">dba_sync()</a></span> will do what they promise for one
database and will do nothing for others. You have to download and install
supported dba-Handlers.
<table class="doctable table">
<caption><strong>List of DBA handlers</strong></caption>
<thead>
<tr>
<th>Handler</th>
<th>Notes</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td><em>dbm</em></td>
<td>
Dbm is the oldest (original) type of Berkeley DB style
databases. You should avoid it, if possible. We do not support
the compatibility functions built into DB2 and gdbm, because
they are only compatible on the source code level, but cannot
handle the original dbm format.
</td>
</tr>
<tr>
<td><em>ndbm</em></td>
<td>
Ndbm is a newer type and more flexible than dbm. It still has
most of the arbitrary limits of dbm (therefore it is
deprecated).
</td>
</tr>
<tr>
<td><em>gdbm</em></td>
<td>
Gdbm is the <a href="ftp://ftp.gnu.org/pub/gnu/gdbm/" class="link external">» GNU database
manager</a>.
</td>
</tr>
<tr>
<td><em>db2</em></td>
<td>
DB2 is for <a href="http://www.sleepycat.com/" class="link external">» Oracle Berkeley
DB 2</a>. It is described as "a programmatic toolkit that
provides high-performance built-in database support for both
standalone and client/server applications."
</td>
</tr>
<tr>
<td><em>db3</em></td>
<td>
DB3 is for <a href="http://www.sleepycat.com/" class="link external">» Oracle Berkeley DB
3</a>.
</td>
</tr>
<tr>
<td><em>db4</em></td>
<td>
DB4 is for <a href="http://www.sleepycat.com/" class="link external">» Oracle Berkeley DB
4 or 5</a>. This option can
be used with BDB 5 as of PHP 5.3.3.
</td>
</tr>
<tr>
<td><em>cdb</em></td>
<td>
Cdb is "a fast, reliable, lightweight package for creating and
reading constant databases." It is from the author of qmail and
can be found at <a href="http://cr.yp.to/cdb.html" class="link external">» http://cr.yp.to/cdb.html</a>. Since it is
constant, we support only reading operations.
We support writing (not updating) through the internal cdb library.
</td>
</tr>
<tr>
<td><em>cdb_make</em></td>
<td>
We support creation (not updating) of cdb files
when the bundled cdb library is used.
</td>
</tr>
<tr>
<td><em>flatfile</em></td>
<td>
This is available for compatibility with the deprecated
<em>dbm</em> extension only and should be avoided.
However you may use this where files were created in this format. That
happens when configure could not find any external library.
</td>
</tr>
<tr>
<td><em>inifile</em></td>
<td>
This is available to be able to modify php.ini files
from within PHP scripts. When working with ini files you can pass arrays
of the form array(0=>group,1=>value_name) or strings of the form
"[group]value_name" where group is optional. As the functions
<span class="function"><a href="function.dba-firstkey.html" class="function">dba_firstkey()</a></span> and <span class="function"><a href="function.dba-nextkey.html" class="function">dba_nextkey()</a></span>
return string representations of the key there is the function
<span class="function"><a href="function.dba-key-split.html" class="function">dba_key_split()</a></span> which allows
to convert the string keys into array keys without loosing <strong><code>FALSE</code></strong>.
</td>
</tr>
<tr>
<td><em>qdbm</em></td>
<td>
The qdbm library can be downloaded from
<a href="http://fallabs.com/qdbm/index.html" class="link external">» http://fallabs.com/qdbm/index.html</a>.
</td>
</tr>
<tr>
<td><em>tcadb</em></td>
<td>
This is available since PHP 5.4.0. The Tokyo Cabinet library can be
downloaded from <a href="http://fallabs.com/tokyocabinet/" class="link external">» http://fallabs.com/tokyocabinet/</a>.
</td>
</tr>
<tr>
<td><em>lmdb</em></td>
<td>
This is available since PHP 7.2.0. The Lightning Memory-Mapped Database library
can be downloaded from <a href="https://symas.com/lmdb/" class="link external">» https://symas.com/lmdb/</a>.
</td>
</tr>
</tbody>
</table>
</p>
<p class="para">
When invoking the <span class="function"><a href="function.dba-open.html" class="function">dba_open()</a></span> or
<span class="function"><a href="function.dba-popen.html" class="function">dba_popen()</a></span> functions, one of the
handler names must be supplied as an argument. The actually
available list of handlers is displayed by invoking
<span class="function"><a href="function.phpinfo.html" class="function">phpinfo()</a></span> or <span class="function"><a href="function.dba-handlers.html" class="function">dba_handlers()</a></span>.
</p>
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