PERF: disable prepared statements

see: https://github.com/rails/rails/issues/21992

app/controllers/admin/diagnostics_controller.rb

@@ -4,6 +4,19 @@ class Admin::DiagnosticsController < Admin::AdminController
   layout false
   skip_before_filter :check_xhr
 
+  def dump_statement_cache
+    statements = Post.exec_sql("select * from pg_prepared_statements").to_a
+    text = ""
+
+    statements.each do |row|
+      text << "name: #{row["name"]} sql: #{row["statement"]}\n"
+    end
+
+    text << "\n\nCOUNT #{statements.count}"
+
+    render text: text, content_type: Mime::TEXT
+  end
+
   def memory_stats
     text = nil
 

config/database.yml

@@ -1,4 +1,5 @@
 development:
+  prepared_statements: false
   adapter: postgresql
   database: discourse_development
   min_messages: warning
@@ -25,6 +26,7 @@ test:
 
 # profile db is used for benchmarking using the script/bench.rb script
 profile:
+  prepared_statements: false
   adapter: postgresql
   database: discourse_profile
   min_messages: warning

config/discourse_defaults.conf

@@ -39,9 +39,9 @@ db_username = discourse
 # password used to access the db
 db_password =
 
-# allow usage of prepared statements, must be disabled for
+# Disallow prepared statements
-# pgpool transaction pooling
+# see: https://github.com/rails/rails/issues/21992
-db_prepared_statements = true
+db_prepared_statements = false
 
 # hostname running the forum
 hostname = "www.example.com"

config/routes.rb

@@ -205,6 +205,7 @@ Discourse::Application.routes.draw do
 
     get "memory_stats"=> "diagnostics#memory_stats", constraints: AdminConstraint.new
     get "dump_heap"=> "diagnostics#dump_heap", constraints: AdminConstraint.new
+    get "dump_statement_cache"=> "diagnostics#dump_statement_cache", constraints: AdminConstraint.new
 
   end # admin namespace