Merge pull request rails#44527 from matthewd/reset-prepared-statements

The database server discards prepared statements when the client disconnects

Author: matthewd

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -549,14 +549,14 @@ def active?
       # new connection with the database. Implementors should call super if they
       # override the default implementation.
       def reconnect!
-        clear_cache!
+        clear_cache!(new_connection: true)
         reset_transaction
       end
 
       # Disconnects from the database if already connected. Otherwise, this
       # method does nothing.
       def disconnect!
-        clear_cache!
+        clear_cache!(new_connection: true)
         reset_transaction
       end
 
@@ -593,8 +593,16 @@ def throw_away!
       end
 
       # Clear any caching the database adapter may be doing.
-      def clear_cache!
-        @lock.synchronize { @statements.clear } if @statements
+      def clear_cache!(new_connection: false)
+        if @statements
+          @lock.synchronize do
+            if new_connection
+              @statements.reset
+            else
+              @statements.clear
+            end
+          end
+        end
       end
 
       # Returns true if its required to reload the connection between requests for development mode.

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -321,23 +321,23 @@ def reload_type_map # :nodoc:
       # Close then reopen the connection.
       def reconnect!
         @lock.synchronize do
-          super
           @connection.reset
           configure_connection
           reload_type_map
+          super
         rescue PG::ConnectionBad
           connect
         end
       end
 
       def reset!
         @lock.synchronize do
-          clear_cache!
           reset_transaction
           unless @connection.transaction_status == ::PG::PQTRANS_IDLE
             @connection.query "ROLLBACK"
           end
           @connection.query "DISCARD ALL"
+          clear_cache!(new_connection: true)
           configure_connection
         end
       end

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

@@ -77,6 +77,8 @@ class SQLite3Adapter < AbstractAdapter
       }
 
       class StatementPool < ConnectionAdapters::StatementPool # :nodoc:
+        alias reset clear
+
         private
           def dealloc(stmt)
             stmt.close unless stmt.closed?

activerecord/lib/active_record/connection_adapters/statement_pool.rb

@@ -42,6 +42,13 @@ def clear
         cache.clear
       end
 
+      # Clear the pool without deallocating; this is only safe when we
+      # know the server has independently deallocated all statements
+      # (e.g. due to a reconnect, or a DISCARD ALL)
+      def reset
+        cache.clear
+      end
+
       def delete(key)
         dealloc cache[key]
         cache.delete(key)