diff --git a/dbms/src/DataStreams/JSONRowOutputStream.cpp b/dbms/src/DataStreams/JSONRowOutputStream.cpp
index 6794ebb52d6..9c43a8fa546 100644
--- a/dbms/src/DataStreams/JSONRowOutputStream.cpp
+++ b/dbms/src/DataStreams/JSONRowOutputStream.cpp
@@ -44,8 +44,6 @@ void JSONRowOutputStream::writePrefix()
 	writeChar('\n', ostr);
 	writeCString("\t\"data\":\n", ostr);
 	writeCString("\t[\n", ostr);
-
-	ostr.next();
 }
 
 
diff --git a/dbms/src/Server/HTTPHandler.cpp b/dbms/src/Server/HTTPHandler.cpp
index 9f4f3690bb4..96434d0777e 100644
--- a/dbms/src/Server/HTTPHandler.cpp
+++ b/dbms/src/Server/HTTPHandler.cpp
@@ -11,7 +11,6 @@
 #include <DB/IO/ConcatReadBuffer.h>
 #include <DB/IO/CompressedReadBuffer.h>
 #include <DB/IO/CompressedWriteBuffer.h>
-#include <DB/IO/WriteBufferFromHTTPServerResponse.h>
 #include <DB/IO/WriteBufferFromString.h>
 #include <DB/IO/WriteHelpers.h>
 
@@ -28,7 +27,7 @@
 namespace DB
 {
 
-void HTTPHandler::processQuery(Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response)
+void HTTPHandler::processQuery(Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response, Output & used_output)
 {
 	LOG_TRACE(log, "Request URI: " << request.getURI());
 
@@ -47,13 +46,12 @@ void HTTPHandler::processQuery(Poco::Net::HTTPServerRequest & request, Poco::Net
 		query_param += '\n';
 
 	/// Если указано compress, то будем сжимать результат.
-	SharedPtr<WriteBufferFromHTTPServerResponse> out = new WriteBufferFromHTTPServerResponse(response);
-	SharedPtr<WriteBuffer> out_maybe_compressed;
+	used_output.out = new WriteBufferFromHTTPServerResponse(response);
 
 	if (parse<bool>(params.get("compress", "0")))
-		out_maybe_compressed = new CompressedWriteBuffer(*out);
+		used_output.out_maybe_compressed = new CompressedWriteBuffer(*used_output.out);
 	else
-		out_maybe_compressed = out;
+		used_output.out_maybe_compressed = used_output.out;
 
 	/// Имя пользователя и пароль могут быть заданы как в параметрах URL, так и с помощью HTTP Basic authentification (и то, и другое не секъюрно).
 	std::string user = params.get("user", "default");
@@ -138,7 +136,7 @@ void HTTPHandler::processQuery(Poco::Net::HTTPServerRequest & request, Poco::Net
 		context.getSettingsRef().limits.readonly = true;
 
 	Stopwatch watch;
-	executeQuery(*in, *out_maybe_compressed, context, query_plan);
+	executeQuery(*in, *used_output.out_maybe_compressed, context, query_plan);
 	watch.stop();
 
 	if (query_plan)
@@ -167,11 +165,13 @@ void HTTPHandler::processQuery(Poco::Net::HTTPServerRequest & request, Poco::Net
 		LOG_INFO(log, "Quota:\n" << quota.toString());
 
 	/// Если не было эксепшена и данные ещё не отправлены - отправляются HTTP заголовки с кодом 200.
-	out->finalize();
+	used_output.out->finalize();
 }
 
 
-void HTTPHandler::trySendExceptionToClient(std::stringstream & s, Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response)
+void HTTPHandler::trySendExceptionToClient(std::stringstream & s,
+	Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response,
+	Output & used_output)
 {
 	try
 	{
@@ -186,8 +186,32 @@ void HTTPHandler::trySendExceptionToClient(std::stringstream & s, Poco::Net::HTT
 		}
 
 		response.setStatusAndReason(Poco::Net::HTTPResponse::HTTP_INTERNAL_SERVER_ERROR);
-		if (!response.sent())
+
+		if (!response.sent() && !used_output.out_maybe_compressed)
+		{
+			/// Ещё ничего не отправляли, и даже не знаем, нужно ли сжимать ответ.
 			response.send() << s.str() << std::endl;
+		}
+		else if (used_output.out_maybe_compressed)
+		{
+			/** Отправим в использованный (возможно сжатый) поток сообщение об ошибке.
+			  * Сообщение об ошибке может идти невпопад - после каких-то данных.
+			  * Также стоит иметь ввиду, что мы могли уже отправить код 200.
+			  */
+
+			/** Если данные есть в буфере, но их ещё не отправили, то и не будем отправлять */
+			if (used_output.out->count() - used_output.out->offset() == 0)
+			{
+				used_output.out_maybe_compressed->position() = used_output.out_maybe_compressed->buffer().begin();
+				used_output.out->position() = used_output.out->buffer().begin();
+			}
+
+			std::string exception_message = s.str();
+			writeString(exception_message, *used_output.out_maybe_compressed);
+			writeChar('\n', *used_output.out_maybe_compressed);
+			used_output.out_maybe_compressed->next();
+			used_output.out->finalize();
+		}
 	}
 	catch (...)
 	{
@@ -198,6 +222,8 @@ void HTTPHandler::trySendExceptionToClient(std::stringstream & s, Poco::Net::HTT
 
 void HTTPHandler::handleRequest(Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response)
 {
+	Output used_output;
+
 	try
 	{
 		bool is_browser = false;
@@ -215,7 +241,7 @@ void HTTPHandler::handleRequest(Poco::Net::HTTPServerRequest & request, Poco::Ne
 		if (request.getVersion() == Poco::Net::HTTPServerRequest::HTTP_1_1)
 			response.setChunkedTransferEncoding(true);
 
-		processQuery(request, response);
+		processQuery(request, response, used_output);
 		LOG_INFO(log, "Done processing query");
 	}
 	catch (Exception & e)
@@ -224,26 +250,26 @@ void HTTPHandler::handleRequest(Poco::Net::HTTPServerRequest & request, Poco::Ne
 		s << "Code: " << e.code()
 			<< ", e.displayText() = " << e.displayText() << ", e.what() = " << e.what();
 		LOG_ERROR(log, s.str());
-		trySendExceptionToClient(s, request, response);
+		trySendExceptionToClient(s, request, response, used_output);
 	}
 	catch (Poco::Exception & e)
 	{
 		std::stringstream s;
 		s << "Code: " << ErrorCodes::POCO_EXCEPTION << ", e.code() = " << e.code()
 			<< ", e.displayText() = " << e.displayText() << ", e.what() = " << e.what();
-		trySendExceptionToClient(s, request, response);
+		trySendExceptionToClient(s, request, response, used_output);
 	}
 	catch (std::exception & e)
 	{
 		std::stringstream s;
 		s << "Code: " << ErrorCodes::STD_EXCEPTION << ". " << e.what();
-		trySendExceptionToClient(s, request, response);
+		trySendExceptionToClient(s, request, response, used_output);
 	}
 	catch (...)
 	{
 		std::stringstream s;
 		s << "Code: " << ErrorCodes::UNKNOWN_EXCEPTION << ". Unknown exception.";
-		trySendExceptionToClient(s, request, response);
+		trySendExceptionToClient(s, request, response, used_output);
 	}
 }
 
diff --git a/dbms/src/Server/HTTPHandler.h b/dbms/src/Server/HTTPHandler.h
index 03c917e57c3..7357c7f5831 100644
--- a/dbms/src/Server/HTTPHandler.h
+++ b/dbms/src/Server/HTTPHandler.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <DB/IO/WriteBufferFromHTTPServerResponse.h>
 #include "Server.h"
 
 
@@ -16,15 +17,26 @@ public:
 	{
 	}
 
+	struct Output
+	{
+		SharedPtr<WriteBufferFromHTTPServerResponse> out;
+		/// Используется для выдачи ответа. Равен либо out, либо CompressedWriteBuffer(*out), в зависимости от настроек.
+		SharedPtr<WriteBuffer> out_maybe_compressed;
+	};
+
 	void handleRequest(Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response);
-	void trySendExceptionToClient(std::stringstream & s, Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response);
+
+	void trySendExceptionToClient(std::stringstream & s,
+		Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response,
+		Output & used_output);
 
 private:
 	Server & server;
 
 	Logger * log;
 
- 	void processQuery(Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response);
+	/// Функция также инициализирует used_output.
+	void processQuery(Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response, Output & used_output);
 };
 
 }
diff --git a/dbms/src/Storages/StorageFactory.cpp b/dbms/src/Storages/StorageFactory.cpp
index 7d8a1507e7b..c9d0fb6f809 100644
--- a/dbms/src/Storages/StorageFactory.cpp
+++ b/dbms/src/Storages/StorageFactory.cpp
@@ -189,7 +189,7 @@ StoragePtr StorageFactory::get(
 	}
 	else if (endsWith(name, "MergeTree"))
 	{
-		/** Движки [Replicated][Summing|Collapsing]MergeTree  (6 комбинаций)
+		/** Движки [Replicated][Summing|Collapsing|Aggregating|]MergeTree  (8 комбинаций)
 		  * В качестве аргумента для движка должно быть указано:
 		  *  - (для Replicated) Путь к таблице в ZooKeeper
 		  *  - (для Replicated) Имя реплики в ZooKeeper