From f0f3deb32b84c87390aa9323597c13818bd6084a Mon Sep 17 00:00:00 2001
From: Guo Xiang Tan <tgx_world@hotmail.com>
Date: Mon, 8 Apr 2019 17:46:49 +0800
Subject: [PATCH] PERF: Simplify query of `UserStat#update_topic_reply_count`.

For a user with alot of posts, we get a 25% speed up.
---
 app/models/user_stat.rb | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/app/models/user_stat.rb b/app/models/user_stat.rb
index e512a942e92..a1b39d551d2 100644
--- a/app/models/user_stat.rb
+++ b/app/models/user_stat.rb
@@ -129,15 +129,11 @@ class UserStat < ActiveRecord::Base
   # topic_reply_count is a count of posts in other users' topics
   def update_topic_reply_count
     self.topic_reply_count =
-        Topic
-      .where(['id in (
-              SELECT topic_id FROM posts p
-              JOIN topics t2 ON t2.id = p.topic_id
-              WHERE p.deleted_at IS NULL AND
-                t2.user_id <> p.user_id AND
-                p.user_id = ?
-              )', self.user_id])
-      .count
+      Topic
+        .joins("INNER JOIN posts ON topics.id = posts.topic_id AND topics.user_id <> posts.user_id")
+        .where("posts.deleted_at IS NULL AND posts.user_id = ?", self.user_id)
+        .distinct
+        .count
   end
 
   MAX_TIME_READ_DIFF = 100