From 2416da997500b381cc3de506ee43d88591355842 Mon Sep 17 00:00:00 2001
From: Bill Harding <wbharding@gmail.com>
Date: Wed, 6 Jan 2021 08:34:37 -0800
Subject: [PATCH] Increment @counter of prepared postgres statements prior to
 running the query. If the next query or the prepared statement itself get
 interrupted, this prevents the database session getting stuck perpetually
 retrying to recreate the same prepared statement.

---
 activerecord/CHANGELOG.md                      |  6 ++++++
 .../connection_adapters/postgresql_adapter.rb  |  6 +-----
 .../adapters/postgresql/statement_pool_test.rb | 18 ++++++++++++++++++
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 8bdc7d2c33..f0b78070f6 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   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*
+
 *   Switch to database adapter return type for `ActiveRecord::Calculations.calculate`
     when called with `:average` (aliased as `ActiveRecord::Calculations.average`)
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index f3243f8884..fd9571af1e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -228,11 +228,7 @@ module ActiveRecord
         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 fef4b02b04..6029630d89 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 @@ module ActiveRecord
       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 @@ module ActiveRecord
           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