APC_WPDB.php

<?php
/**
 * APC-based WordPress Database Access Abstraction Object
 *
 * Extends the wpdb class in order to cache queries in APC
 *
 * Falls back to non-APC database when requesting an admin resource or
 * the query modifies the database.
 *
 * Using something like Memcached might be better as we can namespace
 * the keys and clear them whenever we need to without affecting other apps
 * on the server
 *
 * @link http://codex.wordpress.org/Function_Reference/wpdb_Class
 */
class APC_WPDB extends wpdb {

/**
 * Perform a MySQL database query, using current database connection.
 *
 * More information can be found on the codex page.
 *
 * @since 0.71
 *
 * @param string $query Database query
 * @return int|false Number of rows affected/selected or false on error
 */
	function query( $query ) {
		if ( ! $this->ready )
			return false;

		// some queries are made before the plugins have been
		// loaded, and thus cannot be filtered with this method
		if ( function_exists( 'apply_filters' ) )
			$query = apply_filters( 'query', $query );

		$this->flush();

		// Log how the function was called
		$this->func_call = "\$db->query(\"$query\")";

		// Keep track of the last query for debug..
		$this->last_query = $query;

		if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES )
			$this->timer_start();

		// Don't try caching any database altering queries
		// Or WordPress's lovely SQL_CALC_FOUND_ROWS related-queries
		// This is a performance hit, but wordpress appears to enjoy SQL_CALC_FOUND_ROWS
		// And until they move away from it (never), these queries cannot be safely cached
		// TODO: Cache SQL_CALC_FOUND_ROWS queries via request
		if (preg_match( "/^\\s*(insert|delete|update|replace|alter|FOUND_ROWS) /i", $query) || preg_match("/FOUND_ROWS/i", $query)) {
			return $this->no_cache_query($query);
		}

		$response = $this->getCache($query);
		if ($response === false) {
			return $this->no_cache_query($query);
		}

		// Cache the shit out of this bitch
		$this->num_queries++;
		if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES )
			$this->queries[] = array( $query, $this->timer_stop(), $this->get_caller() );

		$this->col_info    = $response['col_info'];
		$this->last_result = $response['last_result'];
		$this->num_rows    = $response['num_rows'];
		return $response['return'];
	}

/**
 * Performs a regular query against the
 * database without caching the response
 *
 * @param string $query SQL Query being performed
 * @return mixed result of query, or false on error
 */
	function no_cache_query($query) {
		$this->result = @mysql_query( $query, $this->dbh );
		$this->num_queries++;

		if ( defined( 'SAVEQUERIES' ) && SAVEQUERIES )
			$this->queries[] = array( $query, $this->timer_stop(), $this->get_caller() );

		// If there is an error then take note of it..
		if ( $this->last_error = mysql_error( $this->dbh ) ) {
			$this->print_error();
			return false;
		}

		$return_val = 0;
		if ( preg_match( '/^\s*(create|alter|truncate|drop) /i', $query ) ) {
			$return_val = $this->result;
		} elseif ( preg_match( '/^\s*(insert|delete|update|replace) /i', $query ) ) {
			$this->rows_affected = mysql_affected_rows( $this->dbh );
			// Take note of the insert_id
			if ( preg_match( "/^\s*(insert|replace) /i", $query ) ) {
				$this->insert_id = mysql_insert_id($this->dbh);
			}
			// Return number of rows affected
			$return_val = $this->rows_affected;
		} else {
			$i = 0;
			while ( $i < @mysql_num_fields( $this->result ) ) {
				$this->col_info[$i] = @mysql_fetch_field( $this->result );
				$i++;
			}
			$num_rows = 0;
			while ( $row = @mysql_fetch_object( $this->result ) ) {
				$this->last_result[$num_rows] = $row;
				$num_rows++;
			}

			@mysql_free_result( $this->result );

			// Log number of rows the query returned
			// and return number of rows selected
			$this->num_rows = $num_rows;
			$return_val     = $num_rows;
			$this->setCache($query, array(
				'col_info'    => $this->col_info,
				'last_result' => $this->last_result,
				'num_rows'    => $this->num_rows,
				'return'      => $return_val,
			));
		}

		return $return_val;
	}

/**
 * Sets a cache value
 *
 * @param string $key name of unsha'd cache key
 * @param mixed $value value to cache
 * @param int $time time to cache in seconds
 * @return boolean returns the success of the apc value caching
 */
	public function setCache($key, $value, $time = 300) {
		if ($value === false) return false;

		return apc_add(sha1($key), $value, $time);
	}

/**
 * Retrieves a key from cache
 *
 * @param string $key name of unsha'd cache key
 * @return mixed cached resultset pertaining to the key
 */
	public function getCache($key) {
		return apc_fetch(sha1($key));
	}

}

/**
 * Convenience method that can be used to check if caching is possible
 *
 * @return boolean true is the current request is cacheable, false otherwise
 */
function apc_canCacheQueries() {
	if ((defined('WP_ADMIN') && WP_ADMIN) || (defined('DOING_CRON') && DOING_CRON) || (defined('DOING_AJAX') && DOING_AJAX)) {
		return false;
	}

	if (preg_match('/(wp-admin|wp-login|wp-register|wp-signup)/', $_SERVER['REQUEST_URI']) || isset($_GET['preview'])) {
		return false;
	}

	return true;
}

/**
 * Creates a WPDB Object which is APC-based when cacheable and WP-based when not
 */
if (!isset($wpdb)) {
	if (function_exists('apc_fetch') && apc_canCacheQueries()) {
		$wpdb = new APC_WPDB( DB_USER, DB_PASSWORD, DB_NAME, DB_HOST );
	} else {
		$wpdb = new wpdb( DB_USER, DB_PASSWORD, DB_NAME, DB_HOST );
	}
}