Add an index for going from a post to its replies

src/posts/create.js

@@ -82,6 +82,12 @@ module.exports = function (Posts) {
 					function (next) {
 						db.sortedSetAdd('posts:pid', timestamp, postData.pid, next);
 					},
+					function (next) {
+						if (!postData.toPid) {
+							return next(null);
+						}
+						db.sortedSetAdd('pid:' + postData.toPid + ':replies', timestamp, postData.pid, next);
+					},
 					function (next) {
 						db.incrObjectField('global', 'postCount', next);
 					}