class QPCache in QueryPath 6

This is a special-purpose XML cache.

It performs a different role than the built-in Drupal cache. It caches XML documents for any given period. It is not cleared with the Drupal cache. It uses a hashkey for optimal search speed across multiple database types.

The qpcache_* functions in this module are not mere wrappers around the methods here. They add substantial logic on top of the bare caching layer. Part of the logic is the key encoding logic. The QPCache class assumes that keys are strings. The qpcache_* functions provide facilities for use objects and arrays as keys, too.

Hierarchy

• class \QPCache

File

qpcache/qpcache.module, line 197

The main file for qpcache.

class QPCache {

  /**
   * Return true if the cache has this key.
   */
  public static function has($key) {
    list($crc, $hash) = self::genMultiKey($key);
    $now = time();
    $sql = 'SELECT COUNT(hashkey) FROM {qpcache_xmlcache} WHERE crckey=%d AND hashkey=\'%s\' AND (expire = 0 OR expire > %d)';
    return db_result(db_query($sql, $crc, $hash, $now)) > 0;
  }

  /**
   * Return the value of the given key, if it exists in the database.
   *
   * If no value is found, this will return NULL.
   */
  public static function get($key) {
    list($crc, $hash) = self::genMultiKey($key);
    $now = time();

    // if (is_array($key)) {
    //       drupal_set_message('Retrieval key is array.', 'status');
    //     }
    $sql = 'SELECT clearkey, expire, body FROM {qpcache_xmlcache} WHERE crckey=%d AND hashkey=\'%s\' AND (expire = 0 OR expire > %d)';
    $object = db_fetch_object(db_query($sql, $crc, $hash, $now));
    if (empty($object)) {
      return;
    }
    $object->xml = $object->body;
    return $object;
  }

  /**
   * Put a value in the cache.
   *
   * This will overwrite any existing entry with the same key.
   *
   * @param $key
   *   A string value.
   * @param $body
   *   The text value to store.
   * @param $expire
   *   An expiration date in UNIX timestamp format.
   */
  public static function set($key, $body, $expire = 0) {
    list($crckey, $hashkey) = self::genMultiKey($key);

    // foreach (array($key, $body, $expire) as $f) {
    //       if (is_array($f)) {
    //         drupal_set_message('WARNING: Array: ' . print_r($f, TRUE), 'status');
    //       }
    //     }
    db_query("DELETE FROM {qpcache_xmlcache} WHERE hashkey = '%s'", $hashkey);
    db_query("INSERT INTO {qpcache_xmlcache} (crckey, hashkey, clearkey, body, expire) \n      VALUES (%d, '%s', '%s', '%s', %d)", $crckey, $hashkey, $key, $body, $expire);
  }

  /**
   * Remove a single entry from the cache.
   *
   * This will remove the item whether it has expired or note.
   *
   * @param $key
   *   The key of the item to be removed.
   */
  public static function remove($key) {
    list($crckey, $hashkey) = self::genMultiKey($key);
    db_query("DELETE FROM {qpcache_xmlcache} WHERE hashkey = '%s'", $hashkey);
  }

  /**
   * Remove expired keys.
   */
  public static function prune() {
    $now = time();
    db_query('DELETE FROM {qpcache_xmlcache} WHERE expire BETWEEN 1 AND %d', $now);
  }

  /**
   * Empty the cache.
   */
  public static function clear() {
    db_query('TRUNCATE TABLE {qpcache_xmlcache}');
  }

  /**
   * Given the original key, generate a multi-key.
   *
   * For performance reasons, we use a composite key for retrieving entries.
   * This key uses a CRC-32 checksum against the original key plus an MD5 of
   * the original key. A CRC can be looked up in the database about 30 times faster
   * than an MD5. However, it has a much broader collision space.
   * So if indexing is done correctly, we can use the CRC to very quickly narrow,
   * and then use the MD5 to select the appropriate result from a very small set.
   *.
   * @return
   *   List where position 0 is CRC and 1 is MD5
   */
  protected function genMultiKey($key) {
    return array(
      crc32($key),
      md5($key),
    );
  }

}

Members

Name	Modifiers	Type	Description	Overrides
QPCache::clear	public static	function	Empty the cache.
QPCache::genMultiKey	protected	function	Given the original key, generate a multi-key.
QPCache::get	public static	function	Return the value of the given key, if it exists in the database.
QPCache::has	public static	function	Return true if the cache has this key.
QPCache::prune	public static	function	Remove expired keys.
QPCache::remove	public static	function	Remove a single entry from the cache.
QPCache::set	public static	function	Put a value in the cache.