cache noticesWithFriends in memcached

noticesWithFriends is turning out to be one of our most expensive
queries. The join is costly, and this method is hit over and over and
over by desktop clients and other API users.

So, I've added a first pass at caching the results. I store a "window"
of notices -- equal to the first 3 pages of notices, plus one for
pagination -- in the memcached cache. If with-friends notices are
requests, I fetch the whole window out of the cache and grab the slice
requested. If the requested notices are outside the window, we just do
the query. If there's nothing in the cache, we request the window and
store it, then return a slice.

I had to add a NoticeWrapper class that works like DB_DataObject
(well, just the fetch() part...) but just holds an array of notices
instead of a DB cursor.

Finally, saving a new notice blows away the caches for subscribed users.

darcs-hash:20080915065616-84dde-1b1e814c2294498a10b763b779cbb62c3f96aa84.gz

classes/Notice.php

@@ -111,6 +111,27 @@ class Notice extends DB_DataObject
 		
 		common_save_replies($notice);
 		$notice->saveTags();
+
+		# Clear the cache for subscribed users, so they'll update at next request
+		# XXX: someone clever could prepend instead of clearing the cache
+		
+		if (common_config('memcached', 'enabled')) {
+			$cache = new Memcache();
+			if ($cache->connect(common_config('memcached', 'server'), common_config('memcached', 'port'))) {
+				$user = new User();
+		
+				$user->query('SELECT id ' .
+							 'FROM user JOIN subscription ON user.id = subscription.subscriber' .
+							 'WHERE subscription.subscribed = ' . $notice->profile_id);
+
+				while ($user->fetch()) {
+					$cache->delete(common_cache_key('user:notices_with_friends:' . $this->id));
+				}
+				
+				$user->free();
+				unset($user);
+			}
+		}
 		
 		return $notice;
 	}

classes/User.php

@@ -18,11 +18,18 @@
  */
 
 if (!defined('LACONICA')) { exit(1); }
+
+/* We keep the first three 20-notice pages, plus one for pagination check,
+ * in the memcached cache. */
+
+define('WITHFRIENDS_CACHE_WINDOW', 61);
+
 /**
  * Table Definition for user
  */
 require_once 'DB/DataObject.php';
 require_once 'Validate.php';
+require_once($INSTALLDIR.'/lib/noticewrapper.php');
 
 class User extends DB_DataObject 
 {
@@ -134,6 +141,19 @@ class User extends DB_DataObject
 	}
 
 	function noticesWithFriends($offset=0, $limit=20) {
+
+		# We clearly need a more elegant way to make this work.
+		
+		if (common_config('memcached', 'enabled')) {
+			if ($offset + $limit < WITHFRIENDS_CACHE_WINDOW) {
+				$cached = $this->noticesWithFriendsCachedWindow();
+				if (!$cached) {
+					$cached = $this->noticesWithFriendsWindow();
+				}
+				$wrapper = new NoticeWrapper(array_slice($cached, $offset, $limit));
+				return $wrapper;
+			} 
+		}
 		
 		$notice = new Notice();
 		
@@ -146,6 +166,43 @@ class User extends DB_DataObject
 		return $notice;
 	}
 	
+	function noticesWithFriendsCachedWindow() {
+		$cache = new Memcache();
+		$res = $cache->connect(common_config('memcached', 'server'), common_config('memcached', 'port'));
+		if (!$res) {
+			return NULL;
+		}
+		$notices = $cache->get(common_cache_key('user:notices_with_friends:' . $this->id));
+		return $notices;
+	}
+
+	function noticesWithFriendsWindow() {
+		
+		$cache = new Memcache();
+		$res = $cache->connect(common_config('memcached', 'server'), common_config('memcached', 'port'));
+		
+		if (!$res) {
+			return NULL;
+		}
+		
+		$notice = new Notice();
+		
+		$notice->query('SELECT notice.* ' .
+					   'FROM notice JOIN subscription on notice.profile_id = subscription.subscribed ' .
+					   'WHERE subscription.subscriber = ' . $this->id . ' ' .
+					   'ORDER BY created DESC, notice.id DESC ' .
+					   'LIMIT 0, ' . WITHFRIENDS_CACHE_WINDOW);
+		
+		$notices = array();
+		
+		while ($notice->fetch()) {
+			$notices[] = clone($notice);
+		}
+
+		$cache->set(common_cache_key('user:notices_with_friends:' . $this->id), $notices);
+		return $notices;
+	}
+	
 	static function register($fields) {
 
 		# MAGICALLY put fields into current scope

lib/common.php

@@ -97,7 +97,11 @@ $config =
 		'daemon' =>
 		array('piddir' => '/var/run',
 			  'user' => false,
-			  'group' => false)
+			  'group' => false),
+		'memcached' => 
+		array('enabled' => false,
+			  'server' => 'localhost',
+			  'port' => 11211)
 		);
 
 $config['db'] = &PEAR::getStaticProperty('DB_DataObject','options');

lib/noticewrapper.php

@@ -0,0 +1,57 @@
+<?php
+/*
+ * Laconica - a distributed open-source microblogging tool
+ * Copyright (C) 2008, Controlez-Vous, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+if (!defined('LACONICA')) { exit(1); }
+
+class NoticeWrapper {
+
+    public $id;                              // int(4)  primary_key not_null
+    public $profile_id;                      // int(4)   not_null
+    public $uri;                             // varchar(255)  unique_key
+    public $content;                         // varchar(140)  
+    public $rendered;                        // text()  
+    public $url;                             // varchar(255)  
+    public $created;                         // datetime()   not_null
+    public $modified;                        // timestamp()   not_null default_CURRENT_TIMESTAMP
+    public $reply_to;                        // int(4)  
+    public $is_local;                        // tinyint(1)  
+    public $source;                          // varchar(32)  
+
+	var $notices = NULL;
+	var $i = -1;
+	
+	function __construct($arr) {
+		$this->notices = $arr;
+	}
+	
+	function fetch() {
+		static $fields = array('id', 'profile_id', 'uri', 'content', 'rendered',
+							   'url', 'created', 'modified', 'reply_to', 'is_local', 'source');
+		$this->i++;
+		if ($this->i >= array_count($notices)) {
+			return false;
+		} else {
+			$n = $notices[$this->i];
+			foreach ($fields as $f) {
+				$this->$f = $n->$f;
+			}
+			return true;
+		}
+	}
+}

lib/util.php

@@ -1528,3 +1528,13 @@ function common_session_token() {
 	}
 	return $_SESSION['token'];
 }
+
+function common_cache_key($extra) {
+	return 'laconica:' . common_keyize(common_config('site', 'name')) . ':' . $extra;
+}
+
+function common_keyize($str) {
+	$str = strtolower($str);
+	$str = preg_replace('/\s/', '_', $str);
+	return $str;
+}