From ae0625323ac441d3bef49c21313e698447721b48 Mon Sep 17 00:00:00 2001
From: Alan Guo Xiang Tan <gxtan1990@gmail.com>
Date: Wed, 9 Feb 2022 21:48:18 +0800
Subject: [PATCH] FIX: Avoid errors when updating post and topic count user
 stats. (#15876)

In ab5361d69ae4b55a7635676eef7d80dd96d8460c, we rescue from the PG error
but the transaction is already aborted causing any DB query after to
fail. As such, we avoid triggering the error in the first place by
checking that we would not be insertin a negative number into the
counter cache.

Follow-up to ab5361d69ae4b55a7635676eef7d80dd96d8460c
---
 app/services/user_stat_count_updater.rb       | 31 ++++++++++---------
 spec/services/user_stat_count_updater_spec.rb |  7 ++++-
 2 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/app/services/user_stat_count_updater.rb b/app/services/user_stat_count_updater.rb
index 38810e5c689..90866295d7b 100644
--- a/app/services/user_stat_count_updater.rb
+++ b/app/services/user_stat_count_updater.rb
@@ -17,23 +17,24 @@ class UserStatCountUpdater
       return if post.topic.private_message?
       stat = user_stat || post.user.user_stat
 
-      if post.is_first_post?
-        stat.public_send(action, :topic_count)
-      elsif post.post_type == Post.types[:regular]
-        stat.public_send(action, :post_count)
-      end
-    rescue ActiveRecord::StatementInvalid => e
-      if e.cause.is_a?(PG::CheckViolation)
+      column =
+        if post.is_first_post?
+          :topic_count
+        elsif post.post_type == Post.types[:regular]
+          :post_count
+        end
+
+      return if column.blank?
+
+      if action == :decrement! && stat.public_send(column) < 1
         # There are still spots in the code base which results in the counter cache going out of sync. However,
-        # we have a job that runs on a daily basis which will correct the count. Therefore, avoid raising an error for now
-        # and log the exception instead.
-        Discourse.warn_exception(
-          e,
-          message: "Attempted to insert negative count into UserStat#post_count or UserStat#topic_count"
-        )
-      else
-        raise
+        # we have a job that runs on a daily basis which will correct the count. Therefore, we always check that we
+        # wouldn't end up with a negative count first before inserting.
+        Rails.logger.warn("Attempted to insert negative count into UserStat##{column}\n#{caller.join('\n')}")
+        return
       end
+
+      stat.public_send(action, column)
     end
   end
 end
diff --git a/spec/services/user_stat_count_updater_spec.rb b/spec/services/user_stat_count_updater_spec.rb
index a765e97072d..2e60a451103 100644
--- a/spec/services/user_stat_count_updater_spec.rb
+++ b/spec/services/user_stat_count_updater_spec.rb
@@ -6,6 +6,7 @@ describe UserStatCountUpdater do
   fab!(:user) { Fabricate(:user) }
   fab!(:user_stat) { user.user_stat }
   fab!(:post) { Fabricate(:post) }
+  fab!(:post_2) { Fabricate(:post, topic: post.topic) }
 
   before do
     @orig_logger = Rails.logger
@@ -19,6 +20,10 @@ describe UserStatCountUpdater do
   it 'should log the exception when a negative count is inserted' do
     UserStatCountUpdater.decrement!(post, user_stat: user_stat)
 
-    expect(@fake_logger.warnings.first).to include("PG::CheckViolation")
+    expect(@fake_logger.warnings.last).to match("topic_count")
+
+    UserStatCountUpdater.decrement!(post_2, user_stat: user_stat)
+
+    expect(@fake_logger.warnings.last).to match("post_count")
   end
 end