diff --git a/dbms/CMakeLists.txt b/dbms/CMakeLists.txt
index 813c63109fb..c31e52d9823 100644
--- a/dbms/CMakeLists.txt
+++ b/dbms/CMakeLists.txt
@@ -55,6 +55,7 @@ add_headers_and_sources(dbms src/Storages)
 add_headers_and_sources(dbms src/Storages/Distributed)
 add_headers_and_sources(dbms src/Storages/MergeTree)
 add_headers_and_sources(dbms src/Client)
+add_headers_and_sources(dbms src/Processors)
 add_headers_only(dbms src/Server)
 
 list (APPEND clickhouse_common_io_sources ${CONFIG_BUILD})
diff --git a/dbms/src/CMakeLists.txt b/dbms/src/CMakeLists.txt
index d52fb965f9e..9f3c13643f8 100644
--- a/dbms/src/CMakeLists.txt
+++ b/dbms/src/CMakeLists.txt
@@ -14,3 +14,4 @@ add_subdirectory (Server)
 add_subdirectory (Client)
 add_subdirectory (TableFunctions)
 add_subdirectory (Analyzers)
+add_subdirectory (Processors)
diff --git a/dbms/src/Processors/CMakeLists.txt b/dbms/src/Processors/CMakeLists.txt
new file mode 100644
index 00000000000..99ba159eaf4
--- /dev/null
+++ b/dbms/src/Processors/CMakeLists.txt
@@ -0,0 +1,4 @@
+if (ENABLE_TESTS)
+    add_subdirectory (tests)
+endif ()
+
diff --git a/dbms/src/Processors/Processor.h b/dbms/src/Processors/Processor.h
new file mode 100644
index 00000000000..0050eb05994
--- /dev/null
+++ b/dbms/src/Processors/Processor.h
@@ -0,0 +1,564 @@
+#pragma once
+
+#include <list>
+#include <vector>
+#include <memory>
+#include <mutex>
+#include <condition_variable>
+#include <boost/noncopyable.hpp>
+#include <Poco/Event.h>
+#include <Core/Block.h>
+
+
+/** Processor is an element of query execution pipeline.
+  * It has zero or more input ports and zero or more output ports.
+  *
+  * Blocks of data are transferred over ports.
+  * Each port has fixed structure: names and types of columns and values of constants.
+  *
+  * Processors may pull data from input ports, do some processing and push data to output ports.
+  * Processor may indicate that it requires input data to proceed and set priorities of input ports.
+  *
+  * Synchronous work must only use CPU - don't do any sleep, IO wait, network wait.
+  *
+  * Processor may want to do work asynchronously (example: fetch data from remote server)
+  *  - in this case it will initiate background job and allow to subscribe to it.
+  *
+  * Processor may throw an exception to indicate some runtime error.
+  *
+  * Different ports may have different structure. For example, ports may correspond to different datasets.
+  *
+  * TODO Ports may carry algebraic properties about streams of data.
+  * For example, that data comes ordered by specific key; or grouped by specific key; or have unique values of specific key.
+  *
+  * Examples:
+  *
+  * Source. Has no input ports and single output port. Generates data itself and pushes it to its output port.
+  *
+  * Sink. Has single input port and no output ports. Consumes data that was passed to its input port.
+  *
+  * Empty source. Immediately says that data on its output port is finished.
+  *
+  * Null sink. Consumes data and does nothing.
+  *
+  * Simple transformation. Has single input and single output port. Pulls data, transforms it and pushes to output port.
+  * Example: expression calculator.
+  *
+  * Squashing or filtering transformation. Pulls data, possibly accumulates it, and sometimes pushes it to output port.
+  * Examples: DISTINCT, WHERE, squashing of blocks for INSERT SELECT.
+  *
+  * Accumulating transformation. Pulls and accumulates all data from input until it it exhausted, then pushes data to output port.
+  * Examples: ORDER BY, GROUP BY.
+  *
+  * Limiting transformation. Pulls data from input and passes to output.
+  * When there was enough data, says that it doesn't need data on its input and that data on its output port is finished.
+  *
+  * Resize. Has arbitary number of inputs and arbitary number of outputs. Pulls data from whatever ready input and pushes it to randomly choosed output.
+  * Examples:
+  * Union - merge data from number of inputs to one output in arbitary order.
+  * Split - read data from one input and pass it to arbitary output.
+  *
+  * Concat. Has many inputs but only one output. Pulls all data from first input, then all data from second input, etc. and pushes it to output.
+  *
+  * Ordered merge. Has many inputs but only one output. Pulls data from selected input in specific order, merges and pushes it to output.
+  */
+
+namespace DB
+{
+
+class InputPort;
+class OutputPort;
+
+class Port
+{
+protected:
+    friend void connect(OutputPort &, InputPort &);
+
+    /// Shared state of two connected ports.
+    struct State
+    {
+        Block data;
+        bool needed = false;
+        bool finished = false;
+    };
+
+    Block header;
+    std::shared_ptr<State> state;
+
+public:
+    Port(const Block & header)
+        : header(header) {}
+
+    Block getHeader() const { return header; }
+    bool isConnected() const { return state != nullptr; }
+
+    void assumeConnected() const
+    {
+        if (!isConnected())
+            throw Exception("Port is not connected");
+    }
+
+    bool hasData() const
+    {
+        assumeConnected();
+        return state->data;
+    }
+
+    bool isNeeded() const
+    {
+        assumeConnected();
+        return state->needed;
+    }
+};
+
+
+class InputPort : public Port
+{
+public:
+    using Port::Port;
+
+    Block pull()
+    {
+        if (!hasData())
+            throw Exception("Port has no data");
+
+        return std::move(state->data);
+    }
+
+    bool isFinished() const
+    {
+        assumeConnected();
+        return state->finished;
+    }
+
+    void setNeeded()
+    {
+        assumeConnected();
+        state->needed = true;
+    }
+
+    void setNotNeeded()
+    {
+        assumeConnected();
+        state->needed = false;
+    }
+};
+
+
+class OutputPort : public Port
+{
+public:
+    using Port::Port;
+
+    void push(Block && block)
+    {
+        if (hasData())
+            throw Exception("Port already has data");
+
+        state->data = std::move(block);
+    }
+
+    void setFinished()
+    {
+        assumeConnected();
+        state->finished = true;
+    }
+};
+
+
+inline void connect(OutputPort & output, InputPort & input)
+{
+    input.state = output.state = std::make_shared<Port::State>();
+}
+
+
+/** Allow to subscribe for multiple events and wait for them one by one in arbitary order.
+  */
+class EventCounter
+{
+private:
+    size_t events_happened = 0;
+    size_t events_waited = 0;
+
+    mutable std::mutex mutex;
+    std::condition_variable condvar;
+
+public:
+    void notify()
+    {
+        {
+            std::lock_guard lock(mutex);
+            ++events_happened;
+        }
+        condvar.notify_all();
+    }
+
+    void wait()
+    {
+        std::unique_lock lock(mutex);
+        condvar.wait(lock, [&]{ return events_happened > events_waited; });
+        ++events_waited;
+    }
+
+    template <typename Duration>
+    bool waitFor(Duration && duration)
+    {
+        std::unique_lock lock(mutex);
+        if (condvar.wait(lock, std::forward<Duration>(duration), [&]{ return events_happened > events_waited; }))
+        {
+            ++events_waited;
+            return true;
+        }
+        return false;
+    }
+};
+
+
+class IProcessor
+{
+protected:
+    std::list<InputPort> inputs;
+    std::list<OutputPort> outputs;
+
+public:
+    IProcessor() {}
+
+    IProcessor(std::list<InputPort> && inputs, std::list<OutputPort> && outputs)
+        : inputs(std::move(inputs)), outputs(std::move(outputs)) {}
+
+    virtual String getName() const = 0;
+
+    enum class Status
+    {
+        /// Processor needs some data at its inputs to proceed.
+        /// You need to run another processor to generate required input and proceed.
+        NeedData,
+
+        /// Processor cannot proceed because output port is full.
+        /// You need to transfer data from output port to the input port of another processor.
+        PortFull,
+
+        /// All work is done, nothing more to do.
+        Finished,
+
+        /// You may call 'work' method and processor will do some work synchronously.
+        Ready,
+
+        /// You may call 'schedule' method and processor will initiate some background work.
+        Async,
+
+        /// Processor is doing some work in background and you have to wait.
+        Wait
+    };
+
+    virtual Status getStatus() = 0;
+
+    /// You may call this method if 'status' returned Ready.
+    virtual void work()
+    {
+        throw Exception("Method 'work' is not implemented for " + getName() + " processor");
+    }
+
+    /// You may call this method if 'status' returned Async.
+    virtual void schedule(EventCounter & /*watch*/)
+    {
+        throw Exception("Method 'schedule' is not implemented for " + getName() + " processor");
+    }
+
+    virtual ~IProcessor() {}
+
+    /// Someone needs data on at least one output port or it has no outputs.
+    bool isNeeded() const
+    {
+        if (outputs.empty())
+            return true;
+
+        for (const auto & output : outputs)
+            if (output.isNeeded())
+                return true;
+
+        return false;
+    }
+};
+
+using ProcessorPtr = std::shared_ptr<IProcessor>;
+
+
+/** Wraps pipeline in a single processor.
+  * This processor has no inputs and outputs and just executes the pipeline,
+  *  performing all synchronous work from the current thread.
+  */
+class SequentialPipelineExecutor : IProcessor
+{
+private:
+    std::list<ProcessorPtr> processors;
+
+public:
+    SequentialPipelineExecutor(const std::list<ProcessorPtr> & processors) : processors(processors) {}
+
+    String getName() const override { return "SequentialPipelineExecutor"; }
+
+    Status getStatus() override
+    {
+        for (auto & element : processors)
+            if (element->getStatus() == Status::Async)
+                return Status::Async;
+
+        for (auto & element : processors)
+            if (element->getStatus() == Status::Ready && element->isNeeded())
+                return Status::Ready;
+
+        for (auto & element : processors)
+            if (element->getStatus() == Status::Wait)
+                return Status::Wait;
+
+        for (auto & element : processors)
+        {
+            if (element->getStatus() == Status::NeedData)
+                throw Exception("Pipeline stuck: " + element->getName() + " processor need input data but no one is going to generate it");
+            if (element->getStatus() == Status::PortFull)
+                throw Exception("Pipeline stuck: " + element->getName() + " processor have data in output port but no one is going to consume it");
+        }
+
+        /// TODO Check that all processors are finished.
+        return Status::Finished;
+    }
+
+    void work() override
+    {
+        /// Execute one ready and needed processor.
+        for (auto it = processors.begin(); it != processors.end(); ++it)
+        {
+            auto & element = *it;
+
+            //std::cerr << element->getName() << " status is " << static_cast<int>(element->getStatus()) << "\n";
+
+            if (element->getStatus() == Status::Ready && element->isNeeded())
+            {
+                //std::cerr << element->getName() << " will work\n";
+
+                element->work();
+                processors.splice(processors.end(), processors, it);
+                return;
+            }
+        }
+
+        throw Exception("Bad pipeline");
+    }
+
+    void schedule(EventCounter & watch) override
+    {
+        /// Schedule all needed asynchronous jobs.
+        for (auto it = processors.begin(); it != processors.end(); ++it)
+        {
+            auto & element = *it;
+
+            if (element->getStatus() == Status::Async && element->isNeeded())
+                element->schedule(watch);
+        }
+
+        throw Exception("Bad pipeline");
+    }
+};
+
+
+class ISource : public IProcessor
+{
+protected:
+    OutputPort & output;
+    bool finished = false;
+
+    virtual Block generate() = 0;
+
+public:
+    ISource(Block && header)
+        : IProcessor({}, {std::move(header)}), output(outputs.front())
+    {
+    }
+
+    Status getStatus() override
+    {
+        if (finished)
+            return Status::Finished;
+
+        if (output.hasData())
+            return Status::PortFull;
+
+        return Status::Ready;
+    }
+
+    void work() override
+    {
+        if (Block block = generate())
+            output.push(std::move(block));
+        else
+            finished = true;
+    }
+
+    OutputPort & getPort() { return output; }
+};
+
+
+class ISink : public IProcessor
+{
+protected:
+    InputPort & input;
+
+    virtual void consume(Block && block) = 0;
+
+public:
+    ISink(Block && header)
+        : IProcessor({std::move(header)}, {}), input(inputs.front())
+    {
+    }
+
+    Status getStatus() override
+    {
+        if (input.hasData())
+            return Status::Ready;
+
+        if (input.isFinished())
+            return Status::Finished;
+
+        input.setNeeded();
+        return Status::NeedData;
+    }
+
+    void work() override
+    {
+        consume(input.pull());
+    }
+
+    InputPort & getPort() { return input; }
+};
+
+
+/** Has one input and one output.
+  * Simply pull a block from input, transform it, and push it to output.
+  */
+class ITransform : public IProcessor
+{
+protected:
+    InputPort & input;
+    OutputPort & output;
+
+    virtual void transform(Block & block) = 0;
+
+public:
+    ITransform(Block && input_header, Block && output_header)
+        : IProcessor({std::move(input_header)}, {std::move(output_header)}),
+        input(inputs.front()), output(outputs.front())
+    {
+    }
+
+    Status getStatus() override
+    {
+        if (output.hasData())
+            return Status::PortFull;
+
+        if (input.hasData())
+            return Status::Ready;
+
+        if (input.isFinished())
+            return Status::Finished;
+
+        input.setNeeded();
+        return Status::NeedData;
+    }
+
+    void work() override
+    {
+        Block data = input.pull();
+        transform(data);
+        output.push(std::move(data));
+    }
+
+    InputPort & getInputPort() { return input; }
+    OutputPort & getOutputPort() { return output; }
+};
+
+
+class LimitTransform : public IProcessor
+{
+private:
+    InputPort & input;
+    OutputPort & output;
+
+    size_t limit;
+    size_t offset;
+    size_t pos = 0; /// how many rows were read, including the last read block
+    bool always_read_till_end;
+
+public:
+    LimitTransform(Block && header, size_t limit, size_t offset, bool always_read_till_end = false)
+        : IProcessor({std::move(header)}, {std::move(header)}),
+        input(inputs.front()), output(outputs.front()),
+        limit(limit), offset(offset), always_read_till_end(always_read_till_end)
+    {
+    }
+
+    String getName() const override { return "Limit"; }
+
+    Status getStatus() override
+    {
+        if (pos >= offset + limit)
+        {
+            output.setFinished();
+            if (!always_read_till_end)
+            {
+                input.setNotNeeded();
+                return Status::Finished;
+            }
+        }
+
+        if (output.hasData())
+            return Status::PortFull;
+
+        input.setNeeded();
+        return input.hasData()
+            ? Status::Ready
+            : Status::NeedData;
+    }
+
+    void work() override
+    {
+        Block block = input.pull();
+
+        if (pos >= offset + limit)
+            return;
+
+        size_t rows = block.rows();
+        pos += rows;
+
+        if (pos <= offset)
+            return;
+
+        /// return the whole block
+        if (pos >= offset + rows && pos <= offset + limit)
+        {
+            output.push(std::move(block));
+            return;
+        }
+
+        /// return a piece of the block
+        size_t start = std::max(
+            static_cast<Int64>(0),
+            static_cast<Int64>(offset) - static_cast<Int64>(pos) + static_cast<Int64>(rows));
+
+        size_t length = std::min(
+            static_cast<Int64>(limit), std::min(
+            static_cast<Int64>(pos) - static_cast<Int64>(offset),
+            static_cast<Int64>(limit) + static_cast<Int64>(offset) - static_cast<Int64>(pos) + static_cast<Int64>(rows)));
+
+        size_t columns = block.columns();
+        for (size_t i = 0; i < columns; ++i)
+            block.getByPosition(i).column = block.getByPosition(i).column->cut(start, length);
+
+        output.push(std::move(block));
+    }
+
+    InputPort & getInputPort() { return input; }
+    OutputPort & getOutputPort() { return output; }
+};
+
+}
diff --git a/dbms/src/Processors/tests/CMakeLists.txt b/dbms/src/Processors/tests/CMakeLists.txt
new file mode 100644
index 00000000000..7a66dd3d9de
--- /dev/null
+++ b/dbms/src/Processors/tests/CMakeLists.txt
@@ -0,0 +1,2 @@
+add_executable (processors_test processors_test.cpp)
+target_link_libraries (processors_test dbms)
diff --git a/dbms/src/Processors/tests/processors_test.cpp b/dbms/src/Processors/tests/processors_test.cpp
new file mode 100644
index 00000000000..1f9b5b26592
--- /dev/null
+++ b/dbms/src/Processors/tests/processors_test.cpp
@@ -0,0 +1,99 @@
+#include <iostream>
+#include <Processors/Processor.h>
+#include <Columns/ColumnsNumber.h>
+#include <DataTypes/DataTypesNumber.h>
+#include <IO/WriteBufferFromFileDescriptor.h>
+#include <IO/WriteHelpers.h>
+
+
+using namespace DB;
+
+
+class NumbersSource : public ISource
+{
+public:
+    String getName() const override { return "Numbers"; }
+
+    NumbersSource()
+        : ISource(Block({ColumnWithTypeAndName{ ColumnUInt64::create(), std::make_shared<DataTypeUInt64>(), "number" }}))
+    {
+    }
+
+private:
+    UInt64 current_number = 0;
+
+    Block generate() override
+    {
+        MutableColumns columns;
+        columns.emplace_back(ColumnUInt64::create(1, current_number));
+        ++current_number;
+        return getPort().getHeader().cloneWithColumns(std::move(columns));
+    }
+};
+
+
+class PrintSink : public ISink
+{
+public:
+    String getName() const override { return "Print"; }
+
+    PrintSink()
+        : ISink(Block({ColumnWithTypeAndName{ ColumnUInt64::create(), std::make_shared<DataTypeUInt64>(), "number" }}))
+    {
+    }
+
+private:
+    WriteBufferFromFileDescriptor out{STDOUT_FILENO};
+
+    void consume(Block && block) override
+    {
+        size_t rows = block.rows();
+        size_t columns = block.columns();
+
+        for (size_t row_num = 0; row_num < rows; ++row_num)
+        {
+            for (size_t column_num = 0; column_num < columns; ++column_num)
+            {
+                if (column_num != 0)
+                    writeChar('\t', out);
+                getPort().getHeader().getByPosition(column_num).type->serializeText(*block.getByPosition(column_num).column, row_num, out);
+            }
+            writeChar('\n', out);
+        }
+
+        out.next();
+    }
+};
+
+
+int main(int, char **)
+try
+{
+    auto source = std::make_shared<NumbersSource>();
+    auto sink = std::make_shared<PrintSink>();
+    auto limit = std::make_shared<LimitTransform>(source->getPort().getHeader(), 100, 0);
+
+    connect(source->getPort(), limit->getInputPort());
+    connect(limit->getOutputPort(), sink->getPort());
+
+    SequentialPipelineExecutor executor({source, limit, sink});
+
+    while (true)
+    {
+        IProcessor::Status status = executor.getStatus();
+
+        if (status == IProcessor::Status::Finished)
+            break;
+        else if (status == IProcessor::Status::Ready)
+            executor.work();
+        else
+            throw Exception("Bad status");
+    }
+
+    return 0;
+}
+catch (...)
+{
+    std::cerr << getCurrentExceptionMessage(true) << '\n';
+    throw;
+}