Index: antispam.install
===================================================================
--- antispam.install	(revision 349)
+++ antispam.install	(working copy)
@@ -147,3 +147,12 @@
   db_query("DELETE FROM {variable} WHERE name LIKE 'antispam%'");
   cache_clear_all('variables', 'cache');
 }
+
+/**
+ * Add index on `content_id` field so antispam_callback_queue() works reasonably with high node count.
+ */
+function antispam_update_6100(&$sandbox) {
+	$ret = array();
+	db_add_index($ret, 'antispam_spam_marks', 'content_id', array('content_id'));
+	return $ret;
+}