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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@104338 c90b9560-bf6c-de11-be94-00142212c4b1
172 lines
6.1 KiB
XML
172 lines
6.1 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.7 $ -->
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<!-- splitted from ./en/functions/dba.xml, last change in rev 1.2 -->
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<refentry id="function.dba-open">
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<refnamediv>
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<refname>dba_open</refname>
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<refpurpose>Open database</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<methodsynopsis>
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<type>resource</type><methodname>dba_open</methodname>
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<methodparam><type>string</type><parameter>path</parameter></methodparam>
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<methodparam><type>string</type><parameter>mode</parameter></methodparam>
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<methodparam><type>string</type><parameter>handler</parameter></methodparam>
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<methodparam choice="opt"><parameter>...</parameter></methodparam>
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</methodsynopsis>
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<para>
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<function>dba_open</function> establishes a database instance for
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<parameter>path</parameter> with <parameter>mode</parameter> using
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<parameter>handler</parameter>.
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</para>
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<para>
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<parameter>path</parameter> is commonly a regular path in your filesystem.
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</para>
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<para>
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<parameter>mode</parameter> is "r" for read access, "w" for read/write
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access to an already existing database, "c" for read/write access
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and database creation if it doesn't currently exist, and "n" for
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create, truncate and read/write access. Additional you can use "l" to
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lock the database with an .lck file or "d" to lock the databasefile itself.
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It is important that all of your applications do this consistently. If
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you want to test the access and do not want to wait for the lock you can
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add "t".
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</para>
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<para>
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<parameter>handler</parameter> is the <link linkend="dba.requirements">name
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of the handler</link> which shall be
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used for accessing <parameter>path</parameter>. It is passed all optional
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parameters given to <function>dba_open</function> and can act on behalf of
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them.
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</para>
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<para>
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<function>dba_open</function> returns a positive handle or &false;, in
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the case the open is successful or fails, respectively.
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</para>
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<note>
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<para>
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There can only be one writer for one database file. When you use dba on
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a webserver and more than one request requires write operations they can
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only be done one after another. Also read during write is not allowed.
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The dba extension uses locks to prevent this. See the follwoing table:
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<table>
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<title>DBA locking</title>
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<tgroup cols="9">
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<thead>
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<row>
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<entry>already open</entry>
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<entry><parameter>mode</parameter> = "rl"</entry>
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<entry><parameter>mode</parameter> = "rlt"</entry>
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<entry><parameter>mode</parameter> = "wl"</entry>
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<entry><parameter>mode</parameter> = "wlt"</entry>
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<entry><parameter>mode</parameter> = "rd"</entry>
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<entry><parameter>mode</parameter> = "rdt"</entry>
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<entry><parameter>mode</parameter> = "wd"</entry>
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<entry><parameter>mode</parameter> = "wdt"</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>not open</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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</row>
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<row>
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<entry><parameter>mode</parameter> = "rl"</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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<entry>wait</entry>
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<entry>false</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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</row>
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<row>
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<entry><parameter>mode</parameter> = "wl"</entry>
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<entry>wait</entry>
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<entry>false</entry>
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<entry>wait</entry>
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<entry>false</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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</row>
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<row>
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<entry><parameter>mode</parameter> = "rd"</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>ok</entry>
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<entry>ok</entry>
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<entry>wait</entry>
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<entry>false</entry>
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</row>
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<row>
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<entry><parameter>mode</parameter> = "wd"</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>illegal</entry>
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<entry>wait</entry>
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<entry>false</entry>
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<entry>wait</entry>
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<entry>false</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<simplelist>
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<member>ok: the second call will be successfull.</member>
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<member>wait: the second call waits until <function>dba_close</function> is called for the first.</member>
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<member>false: the second call returns false.</member>
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<member>illegal: you must not mix "l" and "d" modifiers for <parameter>mode</parameter> parameter.</member>
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</simplelist>
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</para>
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</note>
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<note>
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<para>
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Locking and the <parameter>mode</parameter> modifiers "l", "d" and "t" were
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added in PHP 4.3.0.
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In PHP versions before PHP 4.3.0 you must use semaphores to guard against
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simultanious database access for any database handler with the exception of
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GDBM. See <link linkend="ref.sem">System V semaphore support</link>.
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</para>
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</note>
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<para>
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See also:
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<function>dba_popen</function>
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<function>dba_close</function>
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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