Merge pull request rails#49802 from composerinteralia/postgres-unrecoverable-connection-error

Recover from failed connections in PostgreSQL

Author: matthewd

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -903,10 +903,10 @@ def exec_cache(sql, name, binds, async:, allow_retry:, materialize_transactions:
 
           update_typemap_for_default_timezone
 
-          stmt_key = prepare_statement(sql, binds)
-          type_casted_binds = type_casted_binds(binds)
-
           with_raw_connection do |conn|
+            stmt_key = prepare_statement(sql, binds, conn)
+            type_casted_binds = type_casted_binds(binds)
+
             log(sql, name, binds, type_casted_binds, stmt_key, async: async) do
               conn.exec_prepared(stmt_key, type_casted_binds)
             end
@@ -956,22 +956,20 @@ def sql_key(sql)
 
         # Prepare the statement if it hasn't been prepared, return
         # the statement key.
-        def prepare_statement(sql, binds)
-          with_raw_connection(allow_retry: true, materialize_transactions: false) do |conn|
-            sql_key = sql_key(sql)
-            unless @statements.key? sql_key
-              nextkey = @statements.next_key
-              begin
-                conn.prepare nextkey, sql
-              rescue => e
-                raise translate_exception_class(e, sql, binds)
-              end
-              # Clear the queue
-              conn.get_last_result
-              @statements[sql_key] = nextkey
+        def prepare_statement(sql, binds, conn)
+          sql_key = sql_key(sql)
+          unless @statements.key? sql_key
+            nextkey = @statements.next_key
+            begin
+              conn.prepare nextkey, sql
+            rescue => e
+              raise translate_exception_class(e, sql, binds)
             end
-            @statements[sql_key]
+            # Clear the queue
+            conn.get_last_result
+            @statements[sql_key] = nextkey
           end
+          @statements[sql_key]
         end
 
         # Connects to a PostgreSQL server and sets up the adapter depending on the

activerecord/test/cases/adapter_test.rb

@@ -612,6 +612,20 @@ def teardown
         assert_predicate @connection, :active?
       end
 
+      test "querying after a failed query restores and succeeds" do
+        Post.first # Connection verified (and prepared statement pool populated if enabled)
+
+        remote_disconnect @connection
+
+        assert_raises(ActiveRecord::ConnectionFailed) do
+          Post.first # Connection no longer verified after failed query
+        end
+
+        assert Post.first # Verifying the connection causes a reconnect and the query succeeds
+
+        assert_predicate @connection, :active?
+      end
+
       test "transaction restores after remote disconnection" do
         remote_disconnect @connection
         Post.transaction do