From 442c6f16f10ea578e1a87717ce6da7f5716cad13 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafael=20Mendon=C3=A7a=20Fran=C3=A7a?=
 <rafael@rubyonrails.org>
Date: Thu, 11 Feb 2021 23:51:53 +0000
Subject: [PATCH] Merge PR #41356

Closes #41356
Closes #41034
---
 activerecord/CHANGELOG.md                      |  7 +++++++
 .../connection_adapters/postgresql_adapter.rb  |  6 +-----
 .../adapters/postgresql/statement_pool_test.rb | 18 ++++++++++++++++++
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index ebb71b529360d..c7909a2f5365f 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Increment postgres prepared statement counter before making a prepared statement, so if the statement is aborted
+    without Rails knowledge (e.g., if app gets kill -9d during long-running query or due to Rack::Timeout), app won't end
+    up in perpetual crash state for being inconsistent with Postgres.
+
+    *wbharding*, *Martin Tepper*
+
+
 ## Rails 6.1.2.1 (February 10, 2021) ##
 
 *   Fix possible DoS vector in PostgreSQL money type
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 54cbc9aaa12c0..4d97ad420af5e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -227,11 +227,7 @@ def initialize(connection, max)
         end
 
         def next_key
-          "a#{@counter + 1}"
-        end
-
-        def []=(sql, key)
-          super.tap { @counter += 1 }
+          "a#{@counter += 1}"
         end
 
         private
diff --git a/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb b/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
index fef4b02b04e1d..6029630d890e6 100644
--- a/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 require "cases/helper"
+require "models/computer"
+require "models/developer"
 
 module ActiveRecord
   module ConnectionAdapters
@@ -16,6 +18,8 @@ def status
       end
 
       class StatementPoolTest < ActiveRecord::PostgreSQLTestCase
+        fixtures :developers
+
         if Process.respond_to?(:fork)
           def test_cache_is_per_pid
             cache = StatementPool.new nil, 10
@@ -37,6 +41,20 @@ def test_dealloc_does_not_raise_on_inactive_connection
           cache["foo"] = "bar"
           assert_nothing_raised { cache.clear }
         end
+
+        def test_prepared_statements_do_not_get_stuck_on_query_interruption
+          pg_connection = ActiveRecord::Base.connection.instance_variable_get(:@connection)
+          pg_connection.stub(:get_last_result, -> { raise "random error" }) do
+            assert_raises(RuntimeError) do
+              Developer.where(name: "David").last
+            end
+
+            # without fix, this raises PG::DuplicatePstatement: ERROR:  prepared statement "a3" already exists
+            assert_raises(RuntimeError) do
+              Developer.where(name: "David").last
+            end
+          end
+        end
       end
     end
   end