Prevent app crash when postgres prepared query keys become out of sync with Rails

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`)
 

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -228,11 +228,7 @@ def initialize(connection, max)
         end
 
         def next_key
-          "a#{@counter + 1}"
-        end
-
-        def []=(sql, key)
-          super.tap { @counter += 1 }
+          "a#{@counter += 1}"
         end
 
         private

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