From abc9b332412921e7ae7f730b23e186bcba412486 Mon Sep 17 00:00:00 2001
From: Evan Prodromou <evan@status.net>
Date: Mon, 4 Jan 2010 10:00:17 -1000
Subject: Memcached_DataObject stores empty values in the cache

There's great value in knowing that something doesn't exist. We
now cache this information, and carefully compare the results from
cache as $results !== false instead of !empty($results), since some
empty values (null, 0, empty array, empty string) are stored in the
cache.

Caching staticGet() and pkeyGet() now store DB misses in the cache,
and cachedQuery() checks for empty results from the cache.
---
 classes/Memcached_DataObject.php | 39 +++++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

(limited to 'classes')

diff --git a/classes/Memcached_DataObject.php b/classes/Memcached_DataObject.php
index 020d813b2..a77e43d38 100644
--- a/classes/Memcached_DataObject.php
+++ b/classes/Memcached_DataObject.php
@@ -19,8 +19,6 @@
 
 if (!defined('STATUSNET') && !defined('LACONICA')) { exit(1); }
 
-require_once INSTALLDIR.'/classes/Memcached_DataObject.php';
-
 class Memcached_DataObject extends DB_DataObject
 {
    /**
@@ -57,7 +55,7 @@ class Memcached_DataObject extends DB_DataObject
             unset($i);
         }
         $i = Memcached_DataObject::getcached($cls, $k, $v);
-        if ($i) {
+        if ($i !== false) { // false == cache miss
             return $i;
         } else {
             $i = DB_DataObject::factory($cls);
@@ -69,6 +67,12 @@ class Memcached_DataObject extends DB_DataObject
                 $i->encache();
                 return $i;
             } else {
+                // save the fact that no such row exists
+                $c = self::memcache();
+                if (!empty($c)) {
+                    $ck = self::cachekey($cls, $k, $v);
+                    $c->set($ck, null);
+                }
                 return false;
             }
         }
@@ -77,10 +81,13 @@ class Memcached_DataObject extends DB_DataObject
     function &pkeyGet($cls, $kv)
     {
         $i = Memcached_DataObject::multicache($cls, $kv);
-        if ($i) {
+        if ($i !== false) { // false == cache miss
             return $i;
         } else {
-            $i = new $cls();
+            $i = DB_DataObject::factory($cls);
+            if (empty($i)) {
+                return false;
+            }
             foreach ($kv as $k => $v) {
                 $i->$k = $v;
             }
@@ -88,6 +95,11 @@ class Memcached_DataObject extends DB_DataObject
                 $i->encache();
             } else {
                 $i = null;
+                $c = self::memcache();
+                if (!empty($c)) {
+                    $ck = self::multicacheKey($cls, $kv);
+                    $c->set($ck, null);
+                }
             }
             return $i;
         }
@@ -220,16 +232,22 @@ class Memcached_DataObject extends DB_DataObject
     function multicache($cls, $kv)
     {
         ksort($kv);
-        $c = Memcached_DataObject::memcache();
+        $c = self::memcache();
         if (!$c) {
             return false;
         } else {
-            $pkeys = implode(',', array_keys($kv));
-            $pvals = implode(',', array_values($kv));
-            return $c->get(Memcached_DataObject::cacheKey($cls, $pkeys, $pvals));
+            return $c->get(self::multicacheKey($cls, $kv));
         }
     }
 
+    static function multicacheKey($cls, $kv)
+    {
+        ksort($kv);
+        $pkeys = implode(',', array_keys($kv));
+        $pvals = implode(',', array_values($kv));
+        return self::cacheKey($cls, $pkeys, $pvals);
+    }
+
     function getSearchEngine($table)
     {
         require_once INSTALLDIR.'/lib/search_engines.php';
@@ -264,7 +282,8 @@ class Memcached_DataObject extends DB_DataObject
         $key_part = common_keyize($cls).':'.md5($qry);
         $ckey = common_cache_key($key_part);
         $stored = $c->get($ckey);
-        if ($stored) {
+
+        if ($stored !== false) {
             return new ArrayWrapper($stored);
         }
 
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