Zend_Db_Profiler can be enabled to allow profiling of queries. Profiles include the queries processed by the adapter as well as elapsed time to run the queries, allowing inspection of the queries that have been performed without needing to add extra debugging code to classes. Advanced usage also allows the developer to filter which queries are profiled.

Enable the profiler by either passing a directive to the adapter constructor, or by asking the adapter to enable it later.

<?php
require_once 'Zend/Db.php';

$params = array (
    'host'     => '127.0.0.1',
    'username' => 'malory',
    'password' => '******',
    'dbname'   => 'camelot',
    'profiler' => true  // turn on profiler; set to false to disable (default)
);

$db = Zend_Db::factory('PDO_MYSQL', $params);

// turn off profiler:
$db->getProfiler()->setEnabled(false);

// turn on profiler:
$db->getProfiler()->setEnabled(true);
?>

At any point, grab the profiler using the adapter's getProfiler() method:

<?php
$profiler = $db->getProfiler();
?>

This returns a Zend_Db_Profiler object instance. With that instance, the developer can examine your queries using a variety of methods:

The return value of getLastQueryProfile() and the individual elements of getQueryProfiles() are Zend_Db_Profiler_Query objects, which provide the ability to inspect the individual queries themselves:

The information Zend_Db_Profiler provides is useful for profiling bottlenecks in applications, and for debugging queries that have been run. For instance, to see the exact query that was last run:

<?php
$query = $profiler->getLastQueryProfile();

echo $query->getQuery();
?>

Perhaps a page is generating slowly; use the profiler to determine first the total number of seconds of all queries, and then step through the queries to find the one that ran longest:

<?php
$totalTime    = $profiler->getTotalElapsedSecs();
$queryCount   = $profiler->getTotalNumQueries();
$longestTime  = 0;
$longestQuery = null;

foreach ($profiler->getQueryProfiles() as $query) {
    if ($query->getElapsedSecs() > $longestTime) {
        $longestTime  = $query->getElapsedSecs();
        $longestQuery = $query->getQuery();
    }
}

echo 'Executed ' . $queryCount . ' queries in ' . $totalTime . ' seconds' . "\n";
echo 'Average query length: ' . $totalTime / $queryCount . ' seconds' . "\n";
echo 'Queries per second: ' . $queryCount / $totalTime . "\n";
echo 'Longest query length: ' . $longestTime . "\n";
echo "Longest query: \n" . $longestQuery . "\n";
?>

In addition to query inspection, the profiler also allows the developer to filter which queries get profiled. The following methods operate on a Zend_Db_Profiler instance:

<?php
// Only profile queries that take at least 5 seconds:
$profiler->setFilterElapsedSecs(5);

// Profile all queries regardless of length:
$profiler->setFilterElapsedSecs(null);
?>

<?php
// profile only SELECT queries
$profiler->setFilterQueryType(Zend_Db_Profiler::SELECT);

// profile SELECT, INSERT, and UPDATE queries
$profiler->setFilterQueryType(Zend_Db_Profiler::SELECT | Zend_Db_Profiler::INSERT | Zend_Db_Profiler::UPDATE);

// profile DELETE queries (so we can figure out why data keeps disappearing)
$profiler->setFilterQueryType(Zend_Db_Profiler::DELETE);

// Remove all filters
$profiler->setFilterQueryType(null);
?>

<?php
// Retrieve only SELECT query profiles
$profiles = $profiler->getQueryProfiles(Zend_Db_Profiler::SELECT);

// Retrieve only SELECT, INSERT, and UPDATE query profiles
$profiles = $profiler->getQueryProfiles(Zend_Db_Profiler::SELECT | Zend_Db_Profiler::INSERT | Zend_Db_Profiler::UPDATE);

// Retrieve DELETE query profiles (so we can figure out why data keeps
// disappearing)
$profiles = $profiler->getQueryProfiles(Zend_Db_Profiler::DELETE);
?>