mirror of
https://github.com/sigmasternchen/php-doc-en
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7f569e1f17
Patch contributed by Sobak <msobaczewski@gmail.com>. git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@350655 c90b9560-bf6c-de11-be94-00142212c4b1
289 lines
8.5 KiB
XML
289 lines
8.5 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<refentry xmlns="http://docbook.org/ns/docbook" xml:id="function.oci-set-prefetch">
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<refnamediv>
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<refname>oci_set_prefetch</refname>
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<refpurpose>Sets number of rows to be prefetched by queries</refpurpose>
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</refnamediv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>bool</type><methodname>oci_set_prefetch</methodname>
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<methodparam><type>resource</type><parameter>statement</parameter></methodparam>
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<methodparam><type>int</type><parameter>rows</parameter></methodparam>
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</methodsynopsis>
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<para>
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Sets the number of rows to be buffered by the Oracle Client
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libraries after a successful query call
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to <function>oci_execute</function> and for each subsequent
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internal fetch request to the database. For queries returning a
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large number of rows, performance can be significantly improved by
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increasing the prefetch count above the
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default <link linkend="ini.oci8.default-prefetch">oci8.default_prefetch</link>
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value.
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</para>
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<para>
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Prefetching is Oracle's efficient way of returning more than one
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data row from the database in each network request. This can
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result in better network and CPU utilization. The buffering of
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rows is internal to OCI8 and the behavior of OCI8 fetching
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functions is unchanged regardless of the prefetch count. For
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example, <function>oci_fetch_row</function> will always return one
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row. The prefetch buffer is per-statement and is not used by
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re-executed statements or by other connections.
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</para>
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<para>
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Call <function>oci_set_prefetch</function> before
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calling <function>oci_execute</function>.
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</para>
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<para>
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A tuning goal is to set the prefetch value to a reasonable size for
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the network and database to handle. For queries returning a very
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large number of rows, overall system efficiency might be better if
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rows are retrieved from the database in several chunks (i.e set the
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prefetch value smaller than the number of rows). This allows the
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database to handle other users' statements while the PHP script is
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processing the current set of rows.
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</para>
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<para>
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Query prefetching was introduced in Oracle 8<emphasis>i</emphasis>. REF CURSOR
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prefetching was introduced in Oracle 11<emphasis>g</emphasis>R2 and occurs when PHP is
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linked with Oracle 11<emphasis>g</emphasis>R2 (or later) Client libraries.
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Nested cursor prefetching was
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introduced in Oracle 11<emphasis>g</emphasis>R2 and requires both the Oracle Client
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libraries and the database to be version 11<emphasis>g</emphasis>R2 or greater.
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</para>
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<para>
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Prefetching is not supported when queries contain LONG or LOB
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columns. The prefetch value is ignored and single-row fetches will
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be used in all the situations when prefetching is not supported.
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</para>
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<para>
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When using Oracle Database 12<emphasis>c</emphasis>, the prefetch
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value set by PHP can be overridden by Oracle's
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client <literal>oraaccess.xml</literal> configuration file. Refer
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to Oracle documentation for more detail.
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</para>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>statement</parameter></term>
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<listitem>
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&oci.arg.statement.id;
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>rows</parameter></term>
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<listitem>
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<para>
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The number of rows to be prefetched, >= 0
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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&return.success;
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</para>
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</refsect1>
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<refsect1 role="changelog">
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&reftitle.changelog;
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<para>
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>&Version;</entry>
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<entry>&Description;</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>PECL OCI8 1.4</entry>
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<entry>
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Before this release, <parameter>rows</parameter> must be >= 1.
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</entry>
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</row>
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<row>
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<entry>PECL OCI8 1.3.4</entry>
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<entry>
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Before this release, prefetching was limited to the lesser
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of <parameter>rows</parameter> rows and 1024
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* <parameter>rows</parameter> bytes. The byte size
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restriction has now been removed.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</para>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title>Changing the default prefetch value for a query</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$conn = oci_connect('hr', 'welcome', 'localhost/XE');
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$stid = oci_parse($conn, 'SELECT * FROM myverybigtable');
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oci_set_prefetch($stid, 300); // Set before calling oci_execute()
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oci_execute($stid);
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echo "<table border='1'>\n";
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while ($row = oci_fetch_array($stid, OCI_ASSOC+OCI_RETURN_NULLS)) {
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echo "<tr>\n";
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foreach ($row as $item) {
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echo " <td>".($item !== null ? htmlentities($item, ENT_QUOTES) : " ")."</td>\n";
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}
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echo "</tr>\n";
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}
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echo "</table>\n";
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oci_free_statement($stid);
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oci_close($conn);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<para>
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<example>
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<title>Changing the default prefetch for a REF CURSOR fetch</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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/*
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Create the PL/SQL stored procedure as:
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CREATE OR REPLACE PROCEDURE myproc(p1 OUT SYS_REFCURSOR) AS
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BEGIN
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OPEN p1 FOR SELECT * FROM all_objects WHERE ROWNUM < 5000;
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END;
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*/
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$conn = oci_connect('hr', 'welcome', 'localhost/XE');
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$stid = oci_parse($conn, 'BEGIN myproc(:rc); END;');
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$refcur = oci_new_cursor($conn);
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oci_bind_by_name($stid, ':rc', $refcur, -1, OCI_B_CURSOR);
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oci_execute($stid);
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// Change the prefetch before executing the cursor.
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// REF CURSOR prefetching works when PHP is linked with Oracle 11gR2 or later Client libraries
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oci_set_prefetch($refcur, 200);
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oci_execute($refcur);
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echo "<table border='1'>\n";
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while ($row = oci_fetch_array($refcur, OCI_ASSOC+OCI_RETURN_NULLS)) {
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echo "<tr>\n";
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foreach ($row as $item) {
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echo " <td>".($item !== null ? htmlentities($item, ENT_QUOTES) : " ")."</td>\n";
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}
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echo "</tr>\n";
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}
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echo "</table>\n";
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oci_free_statement($refcur);
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oci_free_statement($stid);
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oci_close($conn);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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<para>
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If PHP OCI8 fetches from a REF CURSOR and then passes the REF
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CURSOR back to a second PL/SQL procedure for further processing,
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then set the REF CURSOR prefetch count to <constant>0</constant> to
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avoid rows being "lost" from the result set. The prefetch value is
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the number of extra rows fetched in each OCI8 internal request to
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the database, so setting it to <constant>0</constant> means only
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fetch one row at a time.
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<example>
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<title>Setting the prefetch value when passing a REF CURSOR back to Oracle</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$conn = oci_connect('hr', 'welcome', 'localhost/orcl');
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// get the REF CURSOR
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$stid = oci_parse($conn, 'BEGIN myproc(:rc_out); END;');
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$refcur = oci_new_cursor($conn);
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oci_bind_by_name($stid, ':rc_out', $refcur, -1, OCI_B_CURSOR);
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oci_execute($stid);
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// Display two rows, but don't prefetch any extra rows otherwise
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// those extra rows would not be passed back to myproc_use_rc().
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// A prefetch value of 0 is allowed in PHP 5.3.2 and PECL OCI8 1.4
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oci_set_prefetch($refcur, 0);
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oci_execute($refcur);
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$row = oci_fetch_array($refcur);
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var_dump($row);
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$row = oci_fetch_array($refcur);
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var_dump($row);
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// pass the REF CURSOR to myproc_use_rc() to do more data processing
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// with the result set
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$stid = oci_parse($conn, 'begin myproc_use_rc(:rc_in); end;');
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oci_bind_by_name($stid, ':rc_in', $refcur, -1, OCI_B_CURSOR);
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oci_execute($stid);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member>
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<link linkend="ini.oci8.default-prefetch">oci8.default_prefetch</link>
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ini option
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</member>
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</simplelist>
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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:"~/.phpdoc/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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