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

1 files changed, 57 insertions, 0 deletions

diff --git a/classes/User.php b/classes/User.php
index 7eb21eaeb..17b1c9fea 100644
--- a/classes/User.php
+++ b/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