Remove uses of the read replica database.

https://danbooru.donmai.us/forum_topics/9127?page=283#forum_post_160508

There was a recent outage that was caused by the read replica
(yukinoshita.donmai.us) being temporarily unavailable. The pg driver in
rails got hardstuck trying to connect to the replica, which brought down
the whole site. The app servers stopped responding and could only be
brought down with SIGKILL. Even try to boot the rails console didn't
work.

We only really used this to calculate tag counts inside Post.fast_count,
which wasn't really beneficial since the read replica is slower than the
main database.

app/jobs/tag_batch_change_job.rb

@@ -22,7 +22,7 @@ class TagBatchChangeJob < ApplicationJob
 
   def self.estimate_update_count(antecedent, consequent)
     CurrentUser.without_safe_mode do
-      PostReadOnly.tag_match(antecedent).count
+      Post.tag_match(antecedent).count
     end
   end
 

app/logical/post_query_builder.rb

@@ -1,9 +1,8 @@
 class PostQueryBuilder
-  attr_accessor :query_string, :read_only
+  attr_accessor :query_string
 
-  def initialize(query_string, read_only: false)
+  def initialize(query_string)
     @query_string = query_string
-    @read_only = read_only
   end
 
   def add_range_relation(arr, field, relation)
@@ -117,7 +116,7 @@ class PostQueryBuilder
       q = Tag.parse_query(query_string)
     end
 
-    relation = read_only ? PostReadOnly.all : Post.all
+    relation = Post.all
 
     if q[:tag_count].to_i > Danbooru.config.tag_query_limit
       raise ::Post::SearchError

app/models/post.rb

@@ -1129,8 +1129,8 @@ class Post < ApplicationRecord
     end
 
     def fast_count_search(tags, timeout:, raise_on_timeout:)
-      count = PostReadOnly.with_timeout(timeout, nil, tags: tags) do
-        PostReadOnly.tag_match(tags).count
+      count = Post.with_timeout(timeout, nil, tags: tags) do
+        Post.tag_match(tags).count
       end
 
       if count.nil?
@@ -1645,8 +1645,8 @@ class Post < ApplicationRecord
       where("posts.tag_index @@ to_tsquery('danbooru', E?)", tag.to_escaped_for_tsquery)
     end
 
-    def tag_match(query, read_only: false)
-      PostQueryBuilder.new(query, read_only: read_only).build
+    def tag_match(query)
+      PostQueryBuilder.new(query).build
     end
   end
   

app/models/post_read_only.rb

@@ -1,13 +0,0 @@
-class PostReadOnly < Post
-  establish_connection (ENV["RO_DATABASE_URL"] || "ro_#{Rails.env}".to_sym)
-  attr_readonly *column_names
-
-  def with_timeout(n, default_value = nil)
-    connection.execute("SET STATEMENT_TIMEOUT = #{n}") unless Rails.env == "test"
-    yield
-  rescue ::ActiveRecord::StatementInvalid => x
-    return default_value
-  ensure
-    connection.execute("SET STATEMENT_TIMEOUT = 0") unless Rails.env == "test"
-  end
-end

config/docker/compose.yml

@@ -31,7 +31,6 @@ services:
       - SESSION_SECRET_KEY
       - RAILS_ENV
       - DATABASE_URL
-      - RO_DATABASE_URL
       - DEBUG
       - ARCHIVE_DATABASE_URL
       - DANBOORU_AWS_SQS_ARCHIVE_URL

script/install/database.yml.templ

@@ -24,27 +24,6 @@ production:
   timeout: 5000
   url: <%= ENV['DATABASE_URL'] %>
 
-# read only databases, just point to local copies if you have no need
-ro_development:
-  adapter: postgresql
-  database: danbooru2
-  url: <%= ENV['RO_DATABASE_URL'] %>
-
-ro_test:
-  adapter: postgresql
-  database: danbooru2_test
-  url: <%= ENV['RO_DATABASE_URL'] %>
-
-ro_production:
-  adapter: postgresql
-  database: danbooru2
-  url: <%= ENV['RO_DATABASE_URL'] %>
-
-ro_staging:
-  adapter: postgresql
-  database: danbooru2
-  url: <%= ENV['RO_DATABASE_URL'] %>
-
 archive_development:
   adapter: postgresql
   database: archive_development