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<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="performance.database">
<title>Zend_Db Performance</title>
<para>
<classname>Zend_Db</classname> is a database abstraction layer, and is intended to
provide a common <acronym>API</acronym> for <acronym>SQL</acronym> operations.
<classname>Zend_Db_Table</classname> is a
Table Data Gateway, intended to abstract common table-level database
operations. Due to their abstract nature and the "magic" they do under
the hood to perform their operations, they can sometimes introduce
performance overhead.
</para>
<sect2 id="performance.database.tableMetadata">
<title>How can I reduce overhead introduced by Zend_Db_Table for
retrieving table metadata?</title>
<para>
In order to keep usage as simple as possible, and also to support
constantly changing schemas during development,
<classname>Zend_Db_Table</classname> does some magic under the hood: on
first use, it fetches the table schema and stores it within object
members. This operation is typically expensive, regardless of the
database -- which can contribute to bottlenecks in production.
</para>
<para>
Fortunately, there are techniques for improving the situation.
</para>
<sect3 id="performance.database.tableMetadata.cache">
<title>Use the metadata cache</title>
<para>
<classname>Zend_Db_Table</classname> can optionally utilize
<classname>Zend_Cache</classname> to cache table metadata. This is
typically faster to access and less expensive than fetching the
metadata from the database itself.
</para>
<para>
The <link linkend="zend.db.table.metadata.caching"><classname>Zend_Db_Table
</classname> documentation includes information on metadata caching</link>.
</para>
</sect3>
<sect3 id="performance.database.tableMetadata.hardcoding">
<title>Hardcode your metadata in the table definition</title>
<para>
As of 1.7.0, <classname>Zend_Db_Table</classname> also provides <link
linkend="zend.db.table.metadata.caching.hardcoding">support
for hardcoding metadata in the table definition</link>. This is
an advanced use case, and should only be used when you know the
table schema is unlikely to change, or that you're able to keep
the definitions up-to-date.
</para>
</sect3>
</sect2>
<sect2 id="performance.database.select">
<title>
SQL generated with Zend_Db_Select s not hitting my indexes; how can I make it better?
</title>
<para>
<classname>Zend_Db_Select</classname> is relatively good at its job. However,
if you are performing complex queries requiring joins or
sub-selects, it can often be fairly naive.
</para>
<sect3 id="performance.database.select.writeyourown">
<title>Write your own tuned SQL</title>
<para>
The only real answer is to write your own <acronym>SQL</acronym>;
<classname>Zend_Db</classname> does not require the usage of
<classname>Zend_Db_Select</classname>, so providing your own, tuned
<acronym>SQL</acronym> select statements is a perfectly legitimate approach,
</para>
<para>
Run <constant>EXPLAIN</constant> on your queries, and test a variety of
approaches until you can reliably hit your indices in the most
performant way -- and then hardcode the <acronym>SQL</acronym> as a class property
or constant.
</para>
<para>
If the <acronym>SQL</acronym> requires variable arguments, provide placeholders in
the <acronym>SQL</acronym>, and utilize a combination of
<methodname>vsprintf()</methodname> and <methodname>array_map()</methodname> to
inject the values into the <acronym>SQL</acronym>:
</para>
<programlisting language="php"><![CDATA[
// $adapter is the DB adapter. In Zend_Db_Table, retrieve
// it using $this->getAdapter().
$sql = vsprintf(
self::SELECT_FOO,
array_map(array($adapter, 'quoteInto'), $values)
);
]]></programlisting>
</sect3>
</sect2>
</sect1>
<!--
vim:se ts=4 sw=4 et:
-->
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