use replica db for calculating post counts

app/models/post.rb

@@ -1061,8 +1061,8 @@ class Post < ActiveRecord::Base
     end
 
     def fast_count_search(tags, options = {})
-      count = Post.with_timeout(options[:statement_timeout] || 500, nil, :tags => tags) do
+      count = PostReadOnly.with_timeout(3_000, nil) do
-        Post.tag_match(tags).count
+        PostReadOnly.tag_match(tags).count
       end
 
       if count == nil && tags !~ / /
@@ -1083,8 +1083,8 @@ class Post < ActiveRecord::Base
       i = Post.maximum(:id)
       sum = 0
       while i > 0
-        count = Post.with_timeout(options[:statement_timeout] || 500, nil, :tags => tags) do
+        count = PostReadOnly.with_timeout(1_000, nil) do
-          sum += Post.tag_match(tags).where("id <= ? and id > ?", i, i - 25_000).count
+          sum += PostReadOnly.tag_match(tags).where("id <= ? and id > ?", i, i - 25_000).count
           i -= 25_000
         end
 

app/models/post_read_only.rb

@@ -1,4 +1,13 @@
 class PostReadOnly < Post
   establish_connection "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