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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.dba-open" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>dba_open</refname>
<refpurpose>Open database</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type class="union"><type>Dba\Connection</type><type>false</type></type><methodname>dba_open</methodname>
<methodparam><type>string</type><parameter>path</parameter></methodparam>
<methodparam><type>string</type><parameter>mode</parameter></methodparam>
<methodparam choice="opt"><type class="union"><type>string</type><type>null</type></type><parameter>handler</parameter><initializer>&null;</initializer></methodparam>
<methodparam choice="opt"><type>int</type><parameter>permission</parameter><initializer>0644</initializer></methodparam>
<methodparam choice="opt"><type>int</type><parameter>map_size</parameter><initializer>0</initializer></methodparam>
<methodparam choice="opt"><type class="union"><type>int</type><type>null</type></type><parameter>flags</parameter><initializer>&null;</initializer></methodparam>
</methodsynopsis>
<para>
<function>dba_open</function> establishes a database instance for
<parameter>path</parameter> with <parameter>mode</parameter> using
<parameter>handler</parameter>.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>path</parameter></term>
<listitem>
<para>
Commonly a regular path in your filesystem.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>mode</parameter></term>
<listitem>
<para>
It is <literal>r</literal> for read access, <literal>w</literal> for
read/write access to an already existing database, <literal>c</literal>
for read/write access and database creation if it doesn't currently exist,
and <literal>n</literal> for create, truncate and read/write access.
The database is created in BTree mode, other modes (like Hash or Queue)
are not supported.
</para>
<para>
Additionally you can set the database lock method with the next char.
Use <literal>l</literal> to lock the database with a <filename>.lck</filename>
file or <literal>d</literal> to lock the databasefile itself. It is
important that all of your applications do this consistently.
</para>
<para>
If you want to test the access and do not want to wait for the lock
you can add <literal>t</literal> as third character. When you are
absolutely sure that you do not require database locking you can do
so by using <literal>-</literal> instead of <literal>l</literal> or
<literal>d</literal>. When none of <literal>d</literal>,
<literal>l</literal> or <literal>-</literal> is used, dba will lock
on the database file as it would with <literal>d</literal>.
</para>
<note>
<para>
There can only be one writer for one database file. When you use dba on
a web server and more than one request requires write operations they can
only be done one after another. Also read during write is not allowed.
The dba extension uses locks to prevent this. See the following table:
<table>
<title>DBA locking</title>
<tgroup cols="9">
<thead>
<row>
<entry>already open</entry>
<entry><parameter>mode</parameter> = "rl"</entry>
<entry><parameter>mode</parameter> = "rlt"</entry>
<entry><parameter>mode</parameter> = "wl"</entry>
<entry><parameter>mode</parameter> = "wlt"</entry>
<entry><parameter>mode</parameter> = "rd"</entry>
<entry><parameter>mode</parameter> = "rdt"</entry>
<entry><parameter>mode</parameter> = "wd"</entry>
<entry><parameter>mode</parameter> = "wdt"</entry>
</row>
</thead>
<tbody>
<row>
<entry>not open</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>ok</entry>
</row>
<row>
<entry><parameter>mode</parameter> = "rl"</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>wait</entry>
<entry>false</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
</row>
<row>
<entry><parameter>mode</parameter> = "wl"</entry>
<entry>wait</entry>
<entry>false</entry>
<entry>wait</entry>
<entry>false</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
</row>
<row>
<entry><parameter>mode</parameter> = "rd"</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>ok</entry>
<entry>ok</entry>
<entry>wait</entry>
<entry>false</entry>
</row>
<row>
<entry><parameter>mode</parameter> = "wd"</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>illegal</entry>
<entry>wait</entry>
<entry>false</entry>
<entry>wait</entry>
<entry>false</entry>
</row>
</tbody>
</tgroup>
</table>
<simplelist>
<member>ok: the second call will be successful.</member>
<member>wait: the second call waits until <function>dba_close</function> is called for the first.</member>
<member>false: the second call returns false.</member>
<member>illegal: you must not mix <literal>"l"</literal> and <literal>"d"</literal> modifiers for <parameter>mode</parameter> parameter.</member>
</simplelist>
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>handler</parameter></term>
<listitem>
<para>
The name of the <link linkend="dba.requirements">handler</link> which
shall be used for accessing <parameter>path</parameter>. It is passed
all optional parameters given to <function>dba_open</function> and
can act on behalf of them. If <parameter>handler</parameter> is &null;,
then the default handler is invoked.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>permission</parameter></term>
<listitem>
<para>
Optional &integer; parameter which is passed to the driver. It has the same meaning as
the <parameter>permissions</parameter> parameter of <function>chmod</function>,
and defaults to <literal>0644</literal>.
</para>
<para>
The <literal>db1</literal>, <literal>db2</literal>, <literal>db3</literal>,
<literal>db4</literal>, <literal>dbm</literal>, <literal>gdbm</literal>,
<literal>ndbm</literal>, and <literal>lmdb</literal> drivers support the
<parameter>permission</parameter> parameter.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>map_size</parameter></term>
<listitem>
<para>
Optional &integer; parameter which is passed to the driver. Its value should be a multiple of the
page size of the OS, or zero, to use the default map size.
</para>
<para>
Only the <literal>lmdb</literal> driver accepts the <parameter>map_size</parameter> parameter.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>flags</parameter></term>
<listitem>
<para>
Flags to pass to the database drivers. If &null; the default flags will be provided.
Currently, only the LMDB driver supports the following flags
<constant>DBA_LMDB_USE_SUB_DIR</constant> and
<constant>DBA_LMDB_NO_SUB_DIR</constant>.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
Returns a <classname>Dba\Connection</classname> instance on success&return.falseforfailure;.
</para>
</refsect1>
<refsect1 role="errors">
&reftitle.errors;
<para>
&false; is returned and an <constant>E_WARNING</constant> level error is issued when
<parameter>handler</parameter> is &null;, but there is no default handler.
</para>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
<row>
<entry>8.4.0</entry>
<entry>
Returns a <classname>Dba\Connection</classname> instance now;
previously, a &resource; was returned.
</entry>
</row>
<row>
<entry>8.2.0</entry>
<entry>
<parameter>flags</parameter> is added.
</entry>
</row>
<row>
<entry>8.2.0</entry>
<entry>
<parameter>handler</parameter> is now nullable.
</entry>
</row>
<row>
<entry>7.3.14, 7.4.2</entry>
<entry>
The <literal>lmdb</literal> driver now supports an additional <parameter>map_size</parameter>
parameter.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>dba_popen</function></member>
<member><function>dba_close</function></member>
</simplelist>
</para>
</refsect1>
</refentry>
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