diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 4453edb3a7..2adf42c848 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -546,21 +546,34 @@ function clean_page_cache($id) {
 }
 
 function update_post_category_cache($post_ids) {
-	global $wpdb, $category_cache;
+	global $wpdb, $category_cache, $blog_id;
 
 	if ( empty($post_ids) )
 		return;
 
 	if ( is_array($post_ids) )
-		$post_ids = implode(',', $post_ids);
+		$post_id_list = implode(',', $post_ids);
 
-	$dogs = $wpdb->get_results("SELECT post_id, category_id FROM $wpdb->post2cat WHERE post_id IN ($post_ids)");
+	$post_id_array = (array) explode(',', $post_ids);
+	$count = count( $post_id_array);
+	for ( $i = 0; $i < $count; $i++ ) {
+		$post_id = $post_id_array[ $i ];
+		if ( isset( $category_cache[$blog_id][$post_id] ) ) {
+			unset( $post_id_array[ $i ] );
+			continue;
+		}
+	}
+	if ( count( $post_id_array ) == 0 )
+		return;
+	$post_id_list = join( ',', $post_id_array ); // with already cached stuff removed
+
+	$dogs = $wpdb->get_results("SELECT post_id, category_id FROM $wpdb->post2cat WHERE post_id IN ($post_id_list)");
 
 	if ( empty($dogs) )
 		return;
 
 	foreach ($dogs as $catt)
-		$category_cache[$catt->post_id][$catt->category_id] = &get_category($catt->category_id);
+		$category_cache[$blog_id][$catt->post_id][$catt->category_id] = &get_category($catt->category_id);
 }
 
 function update_post_caches(&$posts) {
@@ -590,11 +603,24 @@ function update_postmeta_cache($post_id_list = '') {
 	// We should validate this comma-separated list for the upcoming SQL query
 	$post_id_list = preg_replace('|[^0-9,]|', '', $post_id_list);
 
+	if ( empty( $post_id_list ) )
+		return false;
+
 	// we're marking each post as having its meta cached (with no keys... empty array), to prevent posts with no meta keys from being queried again
 	// any posts that DO have keys will have this empty array overwritten with a proper array, down below
-	$post_id_array = explode(',', $post_id_list);
-	foreach ( (array) $post_id_array as $pid )
-		$post_meta_cache[$pid] = array();
+	$post_id_array = (array) explode(',', $post_id_list);
+	$count = count( $post_id_array);
+	for ( $i = 0; $i < $count; $i++ ) {
+		$post_id = $post_id_array[ $i ];
+		if ( isset( $post_meta_cache[$blog_id][$post_id] ) ) { // If the meta is already cached
+			unset( $post_id_array[ $i ] );
+			continue;
+		}
+		$post_meta_cache[$blog_id][$post_id] = array();
+	}
+	if ( count( $post_id_array ) == 0 )
+		return;
+	$post_id_list = join( ',', $post_id_array ); // with already cached stuff removeds
 
 	// Get post-meta info
 	if ( $meta_list = $wpdb->get_results("SELECT post_id, meta_key, meta_value FROM $wpdb->postmeta WHERE post_id IN($post_id_list) ORDER BY post_id, meta_key", ARRAY_A) ) {
diff --git a/wp-includes/query.php b/wp-includes/query.php
index 8c95cbcd75..aaab66f1c1 100644
--- a/wp-includes/query.php
+++ b/wp-includes/query.php
@@ -1012,9 +1012,10 @@ class WP_Query {
 			}
 		}
 
+		$this->posts = apply_filters('the_posts', $this->posts);
+
 		update_post_caches($this->posts);
 
-		$this->posts = apply_filters('the_posts', $this->posts);
 		$this->post_count = count($this->posts);
 		if ($this->post_count > 0) {
 			$this->post = $this->posts[0];