Split the main WP_Query posts query into two queries to avoid temp tables. Leverage cache to avoid second query in persistent cache environments. Props scribu, cheald, prettyboymp. see #18536

git-svn-id: http://svn.automattic.com/wordpress/trunk@19918 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -3703,3 +3703,26 @@ function wp_debug_backtrace_summary( $ignore_class = null, $skip_frames = 0, $pr
 	else
 		return $caller;
 }
+
+/**
+ * Retrieve ids that are not already present in the cache
+ *
+ * @since 3.4.0
+ *
+ * @param array $object_ids ID list
+ * @param string $cache_key The cache bucket to check against
+ *
+ * @return array
+ */
+function _get_non_cached_ids( $object_ids, $cache_key ) {
+	$clean = array();
+	foreach ( $object_ids as $id ) {
+		$id = (int) $id;
+		if ( !wp_cache_get( $id, $cache_key ) ) {
+			$clean[] = $id;
+		}
+	}
+
+	return $clean;
+}
+