gistfile1.php

<?php
for ($i=1; $i <= 10; $i++) {

$start = microtime(true);

for ($ii=0; $ii < 5000; $ii++) {

  //Pick 8 random tids to search for
  $tids = array();
  for ($iii=0; $iii < 8; $iii++) {
    $tids[] = rand(500, 1000000);
  }

  //Stuff the randomly selected tids into an array compatible with db_query
  $args = array(
    ":tids" => $tids
  );

  //Get a ranked list of the 5 nodes which have the most matches
  $query = db_query("SELECT nid
    FROM taxonomy_index
    WHERE tid
    IN (:tids)", $args);

  $results = $query->fetchAll();
  $result_array = array();
  foreach ($results as $result) {
    $result_array[] = $result->nid;
  }
  arsort(array_count_values($result_array));
  $result_array = array_slice($result_array, 0, 5, true);

}

print "Run $i: " . round(microtime(true) - $start, 3) . ' seconds' . "\n";
}