Content caching in PHP

cache.php
<?php
function cache_start()
{
    global $cache_file_name, $age;

    // a superbly creative way for creating cache files
    $cache_file_name = __FILE__ . '_cache';

    // default cache age
    if (empty($age)) $age = 600;

    // check if cache exists and if the cached data is still valid
    if (@filemtime($cache_file_name) + $age > time()) {
        // Yey! cache hit, output cached data and exit
        readfile($cache_file_name);
        unset($cache_file_name);
        exit;
    }

    // nothing in cache or cache is too old
    ob_start();
}

function cache_end()
{
    global $cache_file_name;

    // nothing to do
    if (empty($cache_file_name)) return;

    // fetch output of the script
    $str = ob_get_clean();

    // output data to the user, so they don't need to wait
    // for the cache writing to complete
    echo $str;
    
    // write to cache
    fwrite(fopen($cache_file_name.'_tmp', "w"), $str);
    // atomic write
    rename($cache_file_name.'_tmp', $cache_file_name);
}

cache_start();

// set cache termination code as the exit handler
// this way we don't need to modify the script
register_shutdown_function("cache_end");
?>


index.php
<?php
    require "./cache.php"; // our cache code

    // Simple guestbook script.
    $db = new sqlite_db("gb.sqlite");
    $r = $db->array_query("SELECT * FROM guestbook", SQLITE_ASSOC);
    foreach ($r as $row) {
        echo $r->user . ' wrote on ' . date("Ymd", $r->date) . ":<br />\n";
        echo $r->message . "<hr /><hr />";
    }
?>

Source:
Performance Tuning PHP
http://talks.php.net/show/perf_tunning/20