Implemented re-readable buffers, add unit tests. [#CLICKHOUSE-2070]

contrib/CMakeLists.txt

@@ -45,3 +45,10 @@ endif ()
 if (NOT AARCH64)
 	add_subdirectory (libcpuid)
 endif ()
+
+if (ENABLE_TESTS)
+	add_subdirectory (googletest)
+	# avoid problems with <regexp.h>
+	target_compile_definitions (gtest INTERFACE -DGTEST_HAS_POSIX_RE=0)
+	target_include_directories (gtest INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/googletest/include)
+endif()

dbms/CMakeLists.txt

@@ -33,6 +33,7 @@ endif ()
 find_package (Threads)
 
 add_subdirectory (src)
+add_subdirectory (tests/unit_tests)
 
 add_library(string_utils
 	include/DB/Common/StringUtils.h

dbms/include/DB/Common/HTMLForm.h

@@ -5,6 +5,8 @@
 #include <Poco/Net/HTTPRequest.h>
 #include <Poco/URI.h>
 
+#include <DB/IO/ReadHelpers.h>
+
 
 /** Somehow, in case of POST, Poco::Net::HTMLForm doesn't read parameters from URL, only from body.
   * This helper allows to read parameters just from URL.
@@ -23,4 +25,18 @@ struct HTMLForm : public Poco::Net::HTMLForm
 		std::istringstream istr(uri.getRawQuery());
 		readUrl(istr);
 	}
+
+
+	template <typename T>
+	T getParsed(const std::string & key, T default_value)
+	{
+		auto it = find(key);
+		return (it != end()) ? DB::parse<T>(it->second) : default_value;
+	}
+
+	template <typename T>
+	T getParsed(const std::string & key)
+	{
+		return DB::parse<T>(get(key));
+	}
 };

dbms/include/DB/IO/MemoryReadWriteBuffer.h

+#include <functional>
+#include <forward_list>
+#include <iostream>
+
+#include <DB/IO/ReadBuffer.h>
+#include <DB/IO/WriteBuffer.h>
+#include <DB/IO/WriteBufferFromFile.h>
+#include <DB/Core/Defines.h>
+#include <DB/Common/Allocator.h>
+#include <DB/Common/Exception.h>
+
+#include <Poco/File.h>
+#include <Poco/Path.h>
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+	extern const int CURRENT_WRITE_BUFFER_IS_EXHAUSTED;
+	extern const int MEMORY_LIMIT_EXCEEDED;
+	extern const int LOGICAL_ERROR;
+}
+
+class CascadeWriteBuffer : public WriteBuffer
+{
+public:
+
+	using WriteBufferPtrs = std::vector<WriteBufferPtr>;
+	using WriteBufferConstructor = std::function<WriteBufferPtr (const WriteBufferPtr & prev_buf)>;
+	using WriteBufferConstructors = std::vector<WriteBufferConstructor>;
+
+	CascadeWriteBuffer(WriteBufferPtrs && prepared_sources_, WriteBufferConstructors && lazy_sources_ = {});
+
+	void nextImpl() override;
+
+	/// Should be called once
+	void getResultBuffers(WriteBufferPtrs & res);
+
+private:
+
+	WriteBuffer * getNextBuffer();
+
+	WriteBufferPtrs prepared_sources;
+	WriteBufferConstructors lazy_sources;
+	size_t first_lazy_source_num;
+	size_t num_sources;
+
+	WriteBuffer * curr_buffer;
+	size_t curr_buffer_num;
+};
+
+
+class ReadBufferFromMemoryWriteBuffer;
+class ReadBufferFromTemporaryWriteBuffer;
+
+
+struct IReadableWriteBuffer
+{
+	/// Creates read buffer from current write buffer
+	/// Returned buffer points to the first byte of original buffer and finds with current position.
+	/// Original stream becomes invalid.
+	virtual std::shared_ptr<ReadBuffer> getReadBuffer() = 0;
+
+	virtual ~IReadableWriteBuffer() {}
+};
+
+
+/// Allow to write large data into memory
+class MemoryWriteBuffer : public WriteBuffer, public IReadableWriteBuffer
+{
+public:
+
+	MemoryWriteBuffer(
+		size_t max_total_size_ = 0,
+		size_t initial_chunk_size_ = DBMS_DEFAULT_BUFFER_SIZE,
+		double growth_rate_ = 2.0);
+
+	void nextImpl() override;
+
+	std::shared_ptr<ReadBuffer> getReadBuffer() override;
+
+	~MemoryWriteBuffer() override;
+
+protected:
+
+	const size_t max_total_size;
+	const size_t initial_chunk_size;
+	const double growth_rate;
+
+	using Container = std::forward_list<BufferBase::Buffer>;
+
+	Container chunk_list;
+	Container::iterator chunk_tail;
+	size_t total_chunks_size = 0;
+
+	void addChunk();
+
+	friend class ReadBufferFromMemoryWriteBuffer;
+};
+
+
+/// Rereadable WriteBuffer, could be used as disk buffer
+/// Creates unique temporary in directory (and directory itself)
+class WriteBufferFromTemporaryFile : public WriteBufferFromFile, public IReadableWriteBuffer
+{
+public:
+	using Ptr = std::shared_ptr<WriteBufferFromTemporaryFile>;
+
+	/// path_template examle "/opt/clickhouse/tmp/data.XXXXXX"
+	static Ptr create(const std::string & path_template_);
+
+	std::shared_ptr<ReadBuffer> getReadBuffer() override;
+
+	~WriteBufferFromTemporaryFile() override;
+
+protected:
+
+	WriteBufferFromTemporaryFile(int fd, const std::string & tmp_path)
+	: WriteBufferFromFile(fd, tmp_path)
+	{}
+};
+
+
+}

dbms/include/DB/IO/ReadBuffer.h

@@ -2,6 +2,7 @@
 
 #include <cstring>
 #include <algorithm>
+#include <memory>
 
 #include <DB/Common/Exception.h>
 #include <DB/IO/BufferBase.h>
@@ -162,4 +163,7 @@ private:
 };
 
 
+using ReadBufferPtr = std::shared_ptr<ReadBuffer>;
+
+
 }

dbms/include/DB/IO/ReadBufferFromFile.h

@@ -20,7 +20,7 @@ namespace DB
   */
 class ReadBufferFromFile : public ReadBufferFromFileDescriptor
 {
-private:
+protected:
 	std::string file_name;
 	CurrentMetrics::Increment metric_increment{CurrentMetrics::OpenFileForRead};
 
@@ -29,7 +29,7 @@ public:
 		char * existing_memory = nullptr, size_t alignment = 0);
 
 	/// Use pre-opened file descriptor.
-	ReadBufferFromFile(int fd, size_t buf_size = DBMS_DEFAULT_BUFFER_SIZE, int flags = -1,
+	ReadBufferFromFile(int fd, const std::string & original_file_name = {}, size_t buf_size = DBMS_DEFAULT_BUFFER_SIZE, int flags = -1,
 		char * existing_memory = nullptr, size_t alignment = 0);
 
 	~ReadBufferFromFile() override;

dbms/include/DB/IO/WriteBuffer.h

@@ -2,6 +2,8 @@
 
 #include <algorithm>
 #include <cstring>
+#include <memory>
+#include <iostream>
 
 #include <DB/Common/Exception.h>
 #include <DB/IO/BufferBase.h>
@@ -96,4 +98,7 @@ private:
 };
 
 
+using WriteBufferPtr = std::shared_ptr<WriteBuffer>;
+
+
 }

dbms/include/DB/IO/WriteBufferFromFile.h

@@ -24,7 +24,7 @@ namespace DB
   */
 class WriteBufferFromFile : public WriteBufferFromFileDescriptor
 {
-private:
+protected:
 	std::string file_name;
 	CurrentMetrics::Increment metric_increment{CurrentMetrics::OpenFileForWrite};
 
@@ -40,9 +40,8 @@ public:
 	/// Use pre-opened file descriptor.
 	WriteBufferFromFile(
 		int fd,
+		const std::string & original_file_name = {},
 		size_t buf_size = DBMS_DEFAULT_BUFFER_SIZE,
-		int flags = -1,
-		mode_t mode = 0666,
 		char * existing_memory = nullptr,
 		size_t alignment = 0);
 

dbms/include/DB/Interpreters/Settings.h

@@ -259,6 +259,11 @@ struct Settings
 	  */ \
 	M(SettingUInt64, input_format_allow_errors_num, 0) \
 	M(SettingFloat, input_format_allow_errors_ratio, 0) \
+	\
+	/** Size of buffer with query results */ \
+	M(SettingUInt64, send_buffer_size, DBMS_DEFAULT_BUFFER_SIZE) \
+	M(SettingUInt64, http_response_memory_buffer_size, 0) \
+	M(SettingString, http_response_memory_buffer_overflow, "") \
 
 	/// Possible limits for query execution.
 	Limits limits;

dbms/src/Core/ErrorCodes.cpp

@@ -364,6 +364,8 @@ namespace ErrorCodes
 	extern const int TABLE_SIZE_EXCEEDS_MAX_DROP_SIZE_LIMIT = 359;
 	extern const int CANNOT_CREATE_CHARSET_CONVERTER = 360;
 	extern const int SEEK_POSITION_OUT_OF_BOUND = 361;
+	extern const int CURRENT_WRITE_BUFFER_IS_EXHAUSTED = 362;
+	extern const int CANNOT_CREATE_IO_BUFFER = 363;
 
 	extern const int KEEPER_EXCEPTION = 999;
 	extern const int POCO_EXCEPTION = 1000;

dbms/src/IO/MemoryReadWriteBuffer.cpp

+#include <DB/IO/MemoryReadWriteBuffer.h>
+#include <DB/IO/ReadBufferFromFile.h>
+#include <DB/IO/WriteBufferFromFile.h>
+#include <DB/Common/Exception.h>
+#include <common/likely.h>
+#include <iostream>
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+	extern const int CURRENT_WRITE_BUFFER_IS_EXHAUSTED;
+	extern const int MEMORY_LIMIT_EXCEEDED;
+	extern const int LOGICAL_ERROR;
+	extern const int CANNOT_OPEN_FILE;
+	extern const int CANNOT_SEEK_THROUGH_FILE;
+	extern const int CANNOT_WRITE_AFTER_END_OF_BUFFER;
+	extern const int CANNOT_CREATE_IO_BUFFER;
+}
+
+
+inline std::ostream & operator << (std::ostream & stream, BufferBase & buffer)
+{
+	stream
+	<< " begin=" << reinterpret_cast<void*>(buffer.buffer().begin())
+	<< " pos=" << buffer.position() - buffer.buffer().begin()
+	<< " size=" << buffer.buffer().size()
+	<< " int_size=" << buffer.internalBuffer().size() << "\n";
+
+	return stream;
+}
+
+
+CascadeWriteBuffer::CascadeWriteBuffer(WriteBufferPtrs && prepared_sources_, WriteBufferConstructors && lazy_sources_)
+	: WriteBuffer(nullptr, 0), prepared_sources(std::move(prepared_sources_)), lazy_sources(std::move(lazy_sources_))
+{
+	first_lazy_source_num = prepared_sources.size();
+	num_sources = first_lazy_source_num + lazy_sources.size();
+
+	/// fill lazy sources by nullptr
+	prepared_sources.resize(num_sources);
+
+	curr_buffer_num = 0;
+	curr_buffer = getNextBuffer();
+	set(curr_buffer->buffer().begin(), curr_buffer->buffer().size());
+}
+
+
+void CascadeWriteBuffer::nextImpl()
+{
+	try
+	{
+		curr_buffer->position() = position();
+		curr_buffer->next();
+	}
+	catch (const Exception & e)
+	{
+		if (curr_buffer_num < num_sources && e.code() == ErrorCodes::CURRENT_WRITE_BUFFER_IS_EXHAUSTED)
+		{
+			/// actualize position of old buffer (it was reset by WriteBuffer::next)
+			curr_buffer->position() = position();
+
+			/// good situation, fetch next WriteBuffer
+			++curr_buffer_num;
+			curr_buffer = getNextBuffer();
+		}
+		else
+			throw;
+	}
+
+	set(curr_buffer->buffer().begin(), curr_buffer->buffer().size());
+}
+
+
+void CascadeWriteBuffer::getResultBuffers(WriteBufferPtrs & res)
+{
+	curr_buffer->position() = position();
+	res = std::move(prepared_sources);
+
+	curr_buffer = nullptr;
+	curr_buffer_num = num_sources = 0;
+}
+
+
+WriteBuffer * CascadeWriteBuffer::getNextBuffer()
+{
+	if (first_lazy_source_num <= curr_buffer_num && curr_buffer_num < num_sources)
+	{
+		if (!prepared_sources[curr_buffer_num])
+		{
+			WriteBufferPtr prev_buf = (curr_buffer_num > 0) ? prepared_sources[curr_buffer_num - 1] : nullptr;
+			prepared_sources[curr_buffer_num] = lazy_sources[curr_buffer_num - first_lazy_source_num](prev_buf);
+		}
+	}
+	else if (curr_buffer_num >= num_sources)
+		throw Exception("There are no WriteBuffers to write result", ErrorCodes::CANNOT_WRITE_AFTER_END_OF_BUFFER);
+
+	WriteBuffer * res = prepared_sources[curr_buffer_num].get();
+	if (!res)
+		throw Exception("Required WriteBuffer is not created", ErrorCodes::CANNOT_CREATE_IO_BUFFER);
+
+	return res;
+}
+
+
+class ReadBufferFromMemoryWriteBuffer : public ReadBuffer
+{
+public:
+
+	ReadBufferFromMemoryWriteBuffer(MemoryWriteBuffer && origin)
+	:
+	ReadBuffer(nullptr, 0),
+	chunk_list(std::move(origin.chunk_list)),
+	end_pos(origin.position())
+	{
+		chunk_head = chunk_list.begin();
+		setChunk();
+	}
+
+	bool nextImpl() override
+	{
+		if (chunk_head == chunk_list.end())
+			return false;
+
+		++chunk_head;
+		return setChunk();
+	}
+
+	~ReadBufferFromMemoryWriteBuffer()
+	{
+		for (const auto & range : chunk_list)
+			Allocator<false>().free(range.begin(), range.size());
+	}
+
+private:
+
+	/// update buffers and position according to chunk_head pointer
+	bool setChunk()
+	{
+		if (chunk_head != chunk_list.end())
+		{
+			internalBuffer() = *chunk_head;
+
+			auto next_chunk = chunk_head;
+			++next_chunk;
+
+			/// It is last chunk, it should be truncated
+			if (next_chunk != chunk_list.end())
+				buffer() = internalBuffer();
+			else
+				buffer() = Buffer(internalBuffer().begin(), end_pos);
+
+			position() = buffer().begin();
+		}
+		else
+		{
+			buffer() = internalBuffer() = Buffer(nullptr, nullptr);
+			position() = nullptr;
+		}
+
+		return buffer().size() != 0;
+	}
+
+	using Container = std::forward_list<BufferBase::Buffer>;
+
+	Container chunk_list;
+	Container::iterator chunk_head;
+	Position end_pos;
+};
+
+
+
+MemoryWriteBuffer::MemoryWriteBuffer(size_t max_total_size_, size_t initial_chunk_size_, double growth_rate_)
+: WriteBuffer(nullptr, 0), max_total_size(max_total_size_), initial_chunk_size(initial_chunk_size_), growth_rate(growth_rate_)
+{
+	addChunk();
+}
+
+void MemoryWriteBuffer::nextImpl()
+{
+	if (unlikely(hasPendingData()))
+	{
+		/// ignore flush
+		buffer() = Buffer(pos, buffer().end());
+		return;
+	}
+
+	addChunk();
+}
+
+void MemoryWriteBuffer::addChunk()
+{
+	size_t next_chunk_size;
+	if (chunk_list.empty())
+	{
+		chunk_tail = chunk_list.before_begin();
+		next_chunk_size = initial_chunk_size;
+	}
+	else
+	{
+		next_chunk_size = std::max(1ul, static_cast<size_t>(chunk_tail->size() * growth_rate));
+	}
+
+	if (max_total_size)
+	{
+		if (total_chunks_size + next_chunk_size > max_total_size)
+			next_chunk_size = max_total_size - total_chunks_size;
+
+		if (0 == next_chunk_size)
+			throw Exception("MemoryWriteBuffer limit is exhausted", ErrorCodes::CURRENT_WRITE_BUFFER_IS_EXHAUSTED);
+	}
+
+	Position begin = reinterpret_cast<Position>(Allocator<false>().alloc(next_chunk_size));
+	chunk_tail = chunk_list.emplace_after(chunk_tail, begin, begin + next_chunk_size);
+	total_chunks_size += next_chunk_size;
+
+	set(chunk_tail->begin(), chunk_tail->size());
+}
+
+std::shared_ptr<ReadBuffer> MemoryWriteBuffer::getReadBuffer()
+{
+	auto res = std::make_shared<ReadBufferFromMemoryWriteBuffer>(std::move(*this));
+
+	/// invalidate members
+	chunk_list.clear();
+	chunk_tail = chunk_list.begin();
+
+	return res;
+}
+
+MemoryWriteBuffer::~MemoryWriteBuffer()
+{
+	for (const auto & range : chunk_list)
+		Allocator<false>().free(range.begin(), range.size());
+}
+
+
+WriteBufferFromTemporaryFile::Ptr WriteBufferFromTemporaryFile::create(const std::string & path_template_)
+{
+	std::string path_template = path_template_;
+
+	if (path_template.empty() || path_template.back() != 'X')
+		path_template += "XXXXXX";
+
+	Poco::File(Poco::Path(path_template).makeParent()).createDirectories();
+
+	int fd = mkstemp(const_cast<char *>(path_template.c_str()));
+	if (fd < 0)
+		throw Exception("Cannot create temporary file " + path_template, ErrorCodes::CANNOT_OPEN_FILE);
+
+	return Ptr(new WriteBufferFromTemporaryFile(fd, path_template));
+}
+
+
+WriteBufferFromTemporaryFile::~WriteBufferFromTemporaryFile()
+{
+	/// remove temporary file if it was not passed to ReadBuffer
+	if (getFD() >= 0 && !getFileName().empty())
+	{
+		Poco::File(getFileName()).remove();
+	}
+}
+
+
+class ReadBufferFromTemporaryWriteBuffer : public ReadBufferFromFile
+{
+public:
+
+	static ReadBufferPtr createFrom(WriteBufferFromTemporaryFile * origin)
+	{
+		int fd = origin->getFD();
+		std::string file_name = origin->getFileName();
+
+		off_t res = lseek(fd, 0, SEEK_SET);
+		if (-1 == res)
+			throwFromErrno("Cannot reread temporary file " + file_name, ErrorCodes::CANNOT_SEEK_THROUGH_FILE);
+
+		return std::make_shared<ReadBufferFromTemporaryWriteBuffer>(fd, file_name);
+	}
+
+	ReadBufferFromTemporaryWriteBuffer(int fd, const std::string & file_name)
+	: ReadBufferFromFile(fd, file_name)
+	{}
+
+	~ReadBufferFromTemporaryWriteBuffer() override
+	{
+		/// remove temporary file
+		Poco::File(file_name).remove();
+	}
+};
+
+ReadBufferPtr WriteBufferFromTemporaryFile::getReadBuffer()
+{
+	/// ignore buffer, write all data to file and reread it from disk
+	sync();
+
+	auto res = ReadBufferFromTemporaryWriteBuffer::createFrom(this);
+
+	/// invalidate FD to avoid close(fd) in destructor
+	setFD(-1);
+	file_name = {};
+
+	return res;
+}
+
+
+}

dbms/src/IO/ReadBufferFromFile.cpp

@@ -61,11 +61,14 @@ ReadBufferFromFile::ReadBufferFromFile(
 
 ReadBufferFromFile::ReadBufferFromFile(
 	int fd,
+	const std::string & original_file_name,
 	size_t buf_size,
 	int flags,
 	char * existing_memory,
 	size_t alignment)
-	: ReadBufferFromFileDescriptor(fd, buf_size, existing_memory, alignment), file_name("(fd = " + toString(fd) + ")")
+	:
+	ReadBufferFromFileDescriptor(fd, buf_size, existing_memory, alignment),
+	file_name(original_file_name.empty() ? "(fd = " + toString(fd) + ")" : original_file_name)
 {
 }
 

dbms/src/IO/WriteBufferFromFile.cpp

@@ -66,12 +66,13 @@ WriteBufferFromFile::WriteBufferFromFile(
 /// Use pre-opened file descriptor.
 WriteBufferFromFile::WriteBufferFromFile(
 	int fd,
+	const std::string & original_file_name,
 	size_t buf_size,
-	int flags,
-	mode_t mode,
 	char * existing_memory,
 	size_t alignment)
-	: WriteBufferFromFileDescriptor(fd, buf_size, existing_memory, alignment), file_name("(fd = " + toString(fd) + ")")
+	:
+	WriteBufferFromFileDescriptor(fd, buf_size, existing_memory, alignment),
+	file_name(original_file_name.empty() ? "(fd = " + toString(fd) + ")" : original_file_name)
 {
 }
 

dbms/src/IO/tests/gtest_cascade_and_memory_write_buffer.cpp

+#include <gtest/gtest.h>
+#include "/home/vludv/ClickHouse/contrib/googletest/include/gtest/gtest.h"
+#include <memory.h>
+
+#include <Poco/File.h>
+
+#include <DB/IO/MemoryReadWriteBuffer.h>
+#include <DB/IO/ConcatReadBuffer.h>
+#include <DB/IO/WriteBufferFromString.h>
+#include <DB/IO/copyData.h>
+
+using namespace DB;
+
+
+static std::string makeTestArray(size_t size)
+{
+	std::string res(size, '\0');
+	for (size_t i = 0; i < res.size(); ++i)
+		res[i] = i % 256;
+	return res;
+}
+
+static void testCascadeBufferRedability(
+	std::string data,
+	CascadeWriteBuffer::WriteBufferPtrs && arg1,
+	CascadeWriteBuffer::WriteBufferConstructors && arg2)
+{
+	CascadeWriteBuffer cascade{std::move(arg1), std::move(arg2)};
+
+	cascade.write(&data[0], data.size());
+	EXPECT_EQ(cascade.count(), data.size());
+
+	std::vector<WriteBufferPtr> write_buffers;
+	std::vector<ReadBufferPtr> read_buffers;
+	std::vector<ReadBuffer *> read_buffers_raw;
+	cascade.getResultBuffers(write_buffers);
+
+	for (WriteBufferPtr & wbuf : write_buffers)
+	{
+		if (!wbuf)
+			continue;
+
+		auto wbuf_readable = dynamic_cast<IReadableWriteBuffer *>(wbuf.get());
+		ASSERT_FALSE(!wbuf_readable);
+
+		auto rbuf = wbuf_readable->getReadBuffer();
+		ASSERT_FALSE(!rbuf);
+
+		read_buffers.emplace_back(rbuf);
+		read_buffers_raw.emplace_back(rbuf.get());
+	}
+
+	ConcatReadBuffer concat(read_buffers_raw);
+	std::string decoded_data;
+	{
+		WriteBufferFromString decoded_data_writer(decoded_data);
+		copyData(concat, decoded_data_writer);
+	}
+
+	ASSERT_EQ(data, decoded_data);
+}
+
+
+TEST(CascadeWriteBuffer, RereadWithTwoMemoryBuffers)
+try
+{
+	size_t max_s = 32;
+	for (size_t s = 0; s < max_s; ++s)
+	{
+		testCascadeBufferRedability(makeTestArray(s),
+			{
+				std::make_shared<MemoryWriteBuffer>(s/2, 1, 2.0),
+				std::make_shared<MemoryWriteBuffer>(s - s/2, 1, 2.0)
+			},
+			{}
+		);
+
+		testCascadeBufferRedability(makeTestArray(s),
+			{
+				std::make_shared<MemoryWriteBuffer>(s, 2, 1.5),
+			},
+			{}
+		);
+
+		testCascadeBufferRedability(makeTestArray(s),
+			{
+				std::make_shared<MemoryWriteBuffer>(0, 1, 1.0),
+			},
+			{}
+		);
+
+		testCascadeBufferRedability(makeTestArray(s),
+			{
+				std::make_shared<MemoryWriteBuffer>(std::max(1ul, s/2), std::max(2ul, s/4), 0.5),
+				std::make_shared<MemoryWriteBuffer>(0, 4, 1.0),
+			},
+			{}
+		);
+
+		testCascadeBufferRedability(makeTestArray(max_s),
+			{
+				std::make_shared<MemoryWriteBuffer>(s, 1, 2.0)
+			},
+			{
+				[=] (auto prev) { return std::make_shared<MemoryWriteBuffer>(max_s - s, 1, 2.0); }
+			}
+		);
+
+		testCascadeBufferRedability(makeTestArray(max_s),
+			{},
+			{
+				[=] (auto prev) { return std::make_shared<MemoryWriteBuffer>(max_s - s, 1, 2.0); },
+				[=] (auto prev) { return std::make_shared<MemoryWriteBuffer>(s, 1, 2.0); }
+			}
+		);
+	}
+}
+catch (const DB::Exception & e)
+{
+	std::cerr << getCurrentExceptionMessage(true) << "\n";
+	throw;
+}
+catch (...)
+{
+	throw;
+}
+
+
+TEST(TemporaryFileWriteBuffer, WriteAndReread)
+try
+{
+	for (size_t s = 0; s < 2500000; s += 500000)
+	{
+		std::string tmp_template = "tmp/TemporaryFileWriteBuffer.XXXXXX";
+		std::string data = makeTestArray(s);
+
+		auto buf = WriteBufferFromTemporaryFile::create(tmp_template);
+		buf->write(&data[0], data.size());
+
+		std::string tmp_filename = buf->getFileName();
+		ASSERT_EQ(tmp_template.size(), tmp_filename.size());
+
+		auto reread_buf = buf->getReadBuffer();
+		std::string decoded_data;
+		{
+			WriteBufferFromString wbuf_decode(decoded_data);
+			copyData(*reread_buf, wbuf_decode);
+		}
+
+		ASSERT_EQ(data.size(), decoded_data.size());
+		ASSERT_TRUE(data == decoded_data);
+
+		buf.reset();
+		reread_buf.reset();
+		ASSERT_TRUE(!Poco::File(tmp_filename).exists());
+	}
+}
+catch (...)
+{
+	std::cerr << getCurrentExceptionMessage(true) << "\n";
+	throw;
+}
+
+
+TEST(CascadeWriteBuffer, RereadWithTemporaryFileWriteBuffer)
+try
+{
+	const std::string tmp_template = "tmp/RereadWithTemporaryFileWriteBuffer.XXXXXX";
+
+	for (size_t s = 0; s < 4000000; s += 1000000)
+	{
+		testCascadeBufferRedability(makeTestArray(s),
+			{},
+			{
+				[=] (auto prev) { return WriteBufferFromTemporaryFile::create(tmp_template); }
+			}
+		);
+
+		testCascadeBufferRedability(makeTestArray(s),
+			{
+				std::make_shared<MemoryWriteBuffer>(std::max(1ul, s/3ul), 2, 1.5),
+			},
+			{
+				[=] (auto prev) { return WriteBufferFromTemporaryFile::create(tmp_template); }
+			}
+		);
+	}
+}
+catch (...)
+{
+	std::cerr << getCurrentExceptionMessage(true) << "\n";
+	throw;
+}

dbms/src/Server/HTTPHandler.cpp

 #include <iomanip>
 
 #include <Poco/Net/HTTPBasicCredentials.h>
+#include <Poco/File.h>
 
 #include <DB/Common/ExternalTable.h>
 #include <DB/Common/StringUtils.h>
+#include <DB/Common/escapeForFileName.h>
 
 #include <DB/IO/ReadBufferFromIStream.h>
 #include <DB/IO/ZlibInflatingReadBuffer.h>
@@ -13,7 +15,11 @@
 #include <DB/IO/CompressedWriteBuffer.h>
 #include <DB/IO/WriteBufferFromString.h>
 #include <DB/IO/WriteBufferFromHTTPServerResponse.h>
+#include <DB/IO/MemoryReadWriteBuffer.h>
+#include <DB/IO/WriteBufferFromFile.h>
 #include <DB/IO/WriteHelpers.h>
+#include <DB/IO/copyData.h>
+#include <DB/IO/ConcatReadBuffer.h>
 
 #include <DB/DataStreams/IProfilingBlockInputStream.h>
 
@@ -36,6 +42,7 @@ namespace ErrorCodes
 	extern const int CANNOT_PARSE_DATE;
 	extern const int CANNOT_PARSE_DATETIME;
 	extern const int CANNOT_PARSE_NUMBER;
+	extern const int CANNOT_OPEN_FILE;
 
 	extern const int UNKNOWN_ELEMENT_IN_AST;
 	extern const int UNKNOWN_TYPE_OF_AST_NODE;
@@ -103,7 +110,8 @@ static Poco::Net::HTTPResponse::HTTPStatus exceptionCodeToHTTPStatus(int excepti
 		return HTTPResponse::HTTP_REQUESTENTITYTOOLARGE;
 	else if (exception_code == ErrorCodes::NOT_IMPLEMENTED)
 		return HTTPResponse::HTTP_NOT_IMPLEMENTED;
-	else if (exception_code == ErrorCodes::SOCKET_TIMEOUT)
+	else if (exception_code == ErrorCodes::SOCKET_TIMEOUT ||
+			 exception_code == ErrorCodes::CANNOT_OPEN_FILE)
 		return HTTPResponse::HTTP_SERVICE_UNAVAILABLE;
 
 	return HTTPResponse::HTTP_INTERNAL_SERVER_ERROR;
@@ -133,6 +141,29 @@ void HTTPHandler::processQuery(
 		query_param += '\n';
 
 
+	/// User name and password can be passed using query parameters or using HTTP Basic auth (both methods are insecure).
+	/// The user and password can be passed by headers (similar to X-Auth-*), which is used by load balancers to pass authentication information
+	std::string user = request.get("X-ClickHouse-User", params.get("user", "default"));
+	std::string password = request.get("X-ClickHouse-Key", params.get("password", ""));
+
+	if (request.hasCredentials())
+	{
+		Poco::Net::HTTPBasicCredentials credentials(request);
+
+		user = credentials.getUsername();
+		password = credentials.getPassword();
+	}
+
+	std::string quota_key = request.get("X-ClickHouse-Quota", params.get("quota_key", ""));
+	std::string query_id = params.get("query_id", "");
+
+	Context context = *server.global_context;
+	context.setGlobalContext(*server.global_context);
+
+	context.setUser(user, password, request.clientAddress(), quota_key);
+	context.setCurrentQueryId(query_id);
+
+
 	/// The client can pass a HTTP header indicating supported compression method (gzip or deflate).
 	String http_response_compression_methods = request.get("Accept-Encoding", "");
 	bool client_supports_http_compression = false;
@@ -154,37 +185,73 @@ void HTTPHandler::processQuery(
 		}
 	}
 
-	used_output.out = std::make_shared<WriteBufferFromHTTPServerResponse>(
-		response, client_supports_http_compression, http_response_compression_method);
-
 	/// Client can pass a 'compress' flag in the query string. In this case the query result is
 	/// compressed using internal algorithm. This is not reflected in HTTP headers.
-	if (parse<bool>(params.get("compress", "0")))
-		used_output.out_maybe_compressed = std::make_shared<CompressedWriteBuffer>(*used_output.out);
-	else
-		used_output.out_maybe_compressed = used_output.out;
+	bool internal_compression = params.getParsed<bool>("compress", false);
 
-	/// User name and password can be passed using query parameters or using HTTP Basic auth (both methods are insecure).
-	/// The user and password can be passed by headers (similar to X-Auth-*), which is used by load balancers to pass authentication information
-	std::string user = request.get("X-ClickHouse-User", params.get("user", "default"));
-	std::string password = request.get("X-ClickHouse-Key", params.get("password", ""));
+	size_t response_buffer_size = params.getParsed<size_t>("buffer_size", DBMS_DEFAULT_BUFFER_SIZE);
+	response_buffer_size = response_buffer_size ? response_buffer_size : DBMS_DEFAULT_BUFFER_SIZE;
 
-	if (request.hasCredentials())
+	auto response_raw = std::make_shared<WriteBufferFromHTTPServerResponse>(
+		response, client_supports_http_compression, http_response_compression_method, response_buffer_size);
+
+	WriteBufferPtr response_maybe_compressed;
+
+	size_t result_buffer_memory_size = params.getParsed<size_t>("result_buffer_size", 0);
+	bool use_memory_buffer = result_buffer_memory_size;
+
+	bool result_buffer_overflow_to_disk = params.get("result_buffer_on_overflow", "http") == "disk";
+
+	if (use_memory_buffer)
 	{
-		Poco::Net::HTTPBasicCredentials credentials(request);
+		ConcatWriteBuffer::WriteBufferPtrs concat_buffers1{ std::make_shared<MemoryWriteBuffer>(result_buffer_memory_size) };
+		ConcatWriteBuffer::WriteBufferConstructors concat_buffers2{};
 
-		user = credentials.getUsername();
-		password = credentials.getPassword();
-	}
+		if (result_buffer_overflow_to_disk)
+		{
+			std::string tmp_path_template = context.getTemporaryPath() + "http_buffers/" + escapeForFileName(user) + ".XXXXXX";
 
-	std::string quota_key = request.get("X-ClickHouse-Quota", params.get("quota_key", ""));
-	std::string query_id = params.get("query_id", "");
+			auto create_tmp_disk_buffer = [tmp_path_template] (const WriteBufferPtr &)
+			{
+				return WriteBufferFromTemporaryFile::create(tmp_path_template);
+			};
 
-	Context context = *server.global_context;
-	context.setGlobalContext(*server.global_context);
+			concat_buffers2.emplace_back(std::move(create_tmp_disk_buffer));
+		}
+		else
+		{
+			auto rewrite_memory_buffer_to_http_and_continue = [response_raw] (const WriteBufferPtr & prev_buf)
+			{
+				auto memory_write_buffer = typeid_cast<MemoryWriteBuffer *>(prev_buf.get());
 
-	context.setUser(user, password, request.clientAddress(), quota_key);
-	context.setCurrentQueryId(query_id);
+				if (!memory_write_buffer)
+					throw Exception("Memory buffer was not allocated", ErrorCodes::LOGICAL_ERROR);
+
+				auto memory_read_buffer = memory_write_buffer->getReadBuffer();
+				copyData(*memory_read_buffer, *response_raw);
+
+				return response_raw;
+			};
+
+			concat_buffers2.emplace_back(rewrite_memory_buffer_to_http_and_continue);
+		}
+
+		used_output.out = response_raw;
+		used_output.delayed_out_raw = std::make_shared<ConcatWriteBuffer>(std::move(concat_buffers1), std::move(concat_buffers2));
+		if (internal_compression)
+			used_output.delayed_out_maybe_compressed = std::make_shared<CompressedWriteBuffer>(*used_output.delayed_out_raw);
+		else
+			used_output.delayed_out_maybe_compressed = used_output.delayed_out_raw;
+		used_output.out_maybe_compressed = used_output.delayed_out_maybe_compressed;
+	}
+	else
+	{
+		used_output.out = response_raw;
+		if (internal_compression)
+			used_output.out_maybe_compressed = std::make_shared<CompressedWriteBuffer>(*response_raw);
+		else
+			used_output.out_maybe_compressed = response_raw;
+	}
 
 	std::unique_ptr<ReadBuffer> in_param = std::make_unique<ReadBufferFromString>(query_param);
 
@@ -268,7 +335,11 @@ void HTTPHandler::processQuery(
 
 	auto readonly_before_query = limits.readonly;
 
-	for (Poco::Net::NameValueCollection::ConstIterator it = params.begin(); it != params.end(); ++it)
+	NameSet reserved_param_names{"query", "compress", "decompress", "user", "password", "quota_key", "query_id", "stacktrace",
+		"buffer_size", "result_buffer_size", "result_buffer_on_overflow"
+	};
+
+	for (auto it = params.begin(); it != params.end(); ++it)
 	{
 		if (it->first == "database")
 		{
@@ -278,14 +349,7 @@ void HTTPHandler::processQuery(
 		{
 			context.setDefaultFormat(it->second);
 		}
-		else if (it->first == "query"
-			|| it->first == "compress"
-			|| it->first == "decompress"
-			|| it->first == "user"
-			|| it->first == "password"
-			|| it->first == "quota_key"
-			|| it->first == "query_id"
-			|| it->first == "stacktrace")
+		else if (reserved_param_names.find(it->first) != reserved_param_names.end())
 		{
 		}
 		else
@@ -346,6 +410,46 @@ void HTTPHandler::processQuery(
 	executeQuery(*in, *used_output.out_maybe_compressed, /* allow_into_outfile = */ false, context,
 		[&response] (const String & content_type) { response.setContentType(content_type); });
 
+	if (use_memory_buffer)
+	{
+		std::vector<WriteBufferPtr> write_buffers;
+		used_output.delayed_out_raw->getResultBuffers(write_buffers);
+
+		std::vector<ReadBufferPtr> read_buffers;
+		ConcatReadBuffer::ReadBuffers read_buffers_raw_ptr;
+		for (auto & write_buf : write_buffers)
+		{
+			IReadableWriteBuffer * write_buf_concrete;
+			if (write_buf && (write_buf_concrete = dynamic_cast<IReadableWriteBuffer *>(write_buf.get())))
+			{
+				read_buffers.emplace_back(write_buf_concrete->getReadBuffer());
+				read_buffers_raw_ptr.emplace_back(read_buffers.back().get());
+			}
+		}
+
+		if (result_buffer_overflow_to_disk)
+		{
+			/// All results in concat buffer
+			if (read_buffers_raw_ptr.empty())
+				throw Exception("There are no buffers to overwrite result into response", ErrorCodes::LOGICAL_ERROR);
+
+			ConcatReadBuffer concat_read_buffer(read_buffers_raw_ptr);
+			copyData(concat_read_buffer, *used_output.out);
+		}
+		else
+		{
+			/// Results could be either in the first buffer, or they could be already pushed to response
+			if (!write_buffers.at(1))
+			{
+				/// Results was not pushed to reponse
+				copyData(*read_buffers.at(0), *used_output.out);
+			}
+		}
+
+		used_output.delayed_out_raw.reset();
+		used_output.delayed_out_maybe_compressed.reset();
+	}
+
 	/// Send HTTP headers with code 200 if no exception happened and the data is still not sent to
 	/// the client.
 	used_output.out->finalize();
@@ -435,16 +539,11 @@ void HTTPHandler::handleRequest(Poco::Net::HTTPServerRequest & request, Poco::Ne
 	{
 		tryLogCurrentException(log);
 
-		std::string exception_message = getCurrentExceptionMessage(with_stacktrace);
-		int exception_code = getCurrentExceptionCode();
-
 		/** If exception is received from remote server, then stack trace is embedded in message.
 		  * If exception is thrown on local server, then stack trace is in separate field.
 		  */
-
-		auto embedded_stack_trace_pos = exception_message.find("Stack trace");
-		if (std::string::npos != embedded_stack_trace_pos && !with_stacktrace)
-			exception_message.resize(embedded_stack_trace_pos);
+		std::string exception_message = getCurrentExceptionMessage(with_stacktrace, true);
+		int exception_code = getCurrentExceptionCode();
 
 		trySendExceptionToClient(exception_message, exception_code, request, response, used_output);
 	}

dbms/src/Server/HTTPHandler.h

@@ -13,6 +13,8 @@ namespace DB
 {
 
 class WriteBufferFromHTTPServerResponse;
+class CascadeWriteBuffer;
+
 
 class HTTPHandler : public Poco::Net::HTTPRequestHandler
 {
@@ -27,6 +29,9 @@ private:
 		std::shared_ptr<WriteBufferFromHTTPServerResponse> out;
 		/// Used for sending response. Points to 'out', or to CompressedWriteBuffer(*out), depending on settings.
 		std::shared_ptr<WriteBuffer> out_maybe_compressed;
+
+		std::shared_ptr<CascadeWriteBuffer> delayed_out_raw;
+		std::shared_ptr<WriteBuffer> delayed_out_maybe_compressed;
 	};
 
 	Server & server;

dbms/tests/unit_tests/CMakeLists.txt

+# Google Test unit tests
+
+# gather all **/gtest*.cpp files with unit tests into single gtest executable. Not CMake-way
+execute_process(COMMAND find ${CMAKE_SOURCE_DIR}/dbms -path "*/tests/gtest*.cpp" -printf "%p;" OUTPUT_VARIABLE sources_with_gtest)
+
+if (ENABLE_TESTS AND sources_with_gtest)
+	add_definitions(-DGTEST_HAS_POSIX_RE=0)
+	add_executable(unit_tests ${sources_with_gtest})
+	target_link_libraries(unit_tests gtest_main dbms)
+	target_include_directories(unit_tests PRIVATE
+		${ClickHouse_SOURCE_DIR}/dbms/include
+	)
+	add_test(unit_tests unit_tests)
+endif()