Reduced memory overhead of preparing LZ4-compressed data for server.

clickhouse/CMakeLists.txt

@@ -1,10 +1,10 @@
 SET ( clickhouse-cpp-lib-src
-    base/coded.cpp
     base/compressed.cpp
     base/input.cpp
     base/output.cpp
     base/platform.cpp
     base/socket.cpp
+    base/wire_format.cpp
 
     columns/array.cpp
     columns/date.cpp

clickhouse/base/compressed.cpp

@@ -1,16 +1,24 @@
 #include "compressed.h"
 #include "wire_format.h"
+#include "output.h"
 
 #include <cityhash/city.h>
 #include <lz4/lz4.h>
 #include <stdexcept>
 #include <system_error>
 
-#define DBMS_MAX_COMPRESSED_SIZE    0x40000000ULL   // 1GB
+namespace {
+constexpr size_t HEADER_SIZE = 9;
+// see DB::CompressionMethodByte::LZ4 from src/Compression/CompressionInfo.h of ClickHouse project
+constexpr uint8_t COMPRESSION_METHOD = 0x82;
+// Documentation says that compression is faster when output buffer is larger than LZ4_compressBound estimation.
+constexpr size_t EXTRA_COMPRESS_BUFFER_SIZE = 4096;
+constexpr size_t DBMS_MAX_COMPRESSED_SIZE = 0x40000000ULL;   // 1GB
+}
 
 namespace clickhouse {
 
-CompressedInput::CompressedInput(CodedInputStream* input)
+CompressedInput::CompressedInput(InputStream* input)
     : input_(input)
 {
 }
@@ -22,7 +30,7 @@ CompressedInput::~CompressedInput() {
 #else
         if (!std::uncaught_exceptions()) {
 #endif
-            throw std::runtime_error("some data was not readed");
+            throw std::runtime_error("some data was not read");
         }
     }
 }
@@ -50,9 +58,8 @@ bool CompressedInput::Decompress() {
         return false;
     }
 
-    if (method != 0x82) {
-        throw std::runtime_error("unsupported compression method " +
-                                 std::to_string(int(method)));
+    if (method != COMPRESSION_METHOD) {
+        throw std::runtime_error("unsupported compression method " + std::to_string(int(method)));
     } else {
         if (!WireFormat::ReadFixed(input_, &compressed)) {
             return false;
@@ -75,7 +82,7 @@ bool CompressedInput::Decompress() {
             out.Write(&original,   sizeof(original));
         }
 
-        if (!WireFormat::ReadBytes(input_, tmp.data() + 9, compressed - 9)) {
+        if (!WireFormat::ReadBytes(input_, tmp.data() + HEADER_SIZE, compressed - HEADER_SIZE)) {
             return false;
         } else {
             if (hash != CityHash128((const char*)tmp.data(), compressed)) {
@@ -85,7 +92,7 @@ bool CompressedInput::Decompress() {
 
         data_ = Buffer(original);
 
-        if (LZ4_decompress_safe((const char*)tmp.data() + 9, (char*)data_.data(), compressed - 9, original) < 0) {
+        if (LZ4_decompress_safe((const char*)tmp.data() + HEADER_SIZE, (char*)data_.data(), compressed - HEADER_SIZE, original) < 0) {
             throw std::runtime_error("can't decompress data");
         } else {
             mem_.Reset(data_.data(), original);
@@ -95,4 +102,73 @@ bool CompressedInput::Decompress() {
     return true;
 }
 
+
+CompressedOutput::CompressedOutput(OutputStream * destination, size_t max_compressed_chunk_size)
+    : destination_(destination)
+    , max_compressed_chunk_size_(max_compressed_chunk_size)
+{
+    PreallocateCompressBuffer(max_compressed_chunk_size);
+}
+
+CompressedOutput::~CompressedOutput() {
+    Flush();
+}
+
+size_t CompressedOutput::DoWrite(const void* data, size_t len) {
+    const size_t original_len = len;
+    // what if len > max_compressed_chunk_size_ ?
+    const size_t max_chunk_size = max_compressed_chunk_size_ > 0 ? max_compressed_chunk_size_ : len;
+    if (max_chunk_size > max_compressed_chunk_size_) {
+        PreallocateCompressBuffer(len);
+    }
+
+    while (len > 0) {
+        auto to_compress = std::min(len, max_chunk_size);
+        Compress(data, to_compress);
+
+        len -= to_compress;
+        data = reinterpret_cast<const char*>(data) + to_compress;
+    }
+
+    return original_len - len;
+}
+
+void CompressedOutput::DoFlush() {
+    destination_->Flush();
+}
+
+void CompressedOutput::Compress(const void * data, size_t len) {
+    const auto compressed_size = LZ4_compress_default(
+            (const char*)data,
+            (char*)compressed_buffer_.data() + HEADER_SIZE,
+            len,
+            compressed_buffer_.size() - HEADER_SIZE);
+    if (compressed_size <= 0)
+        throw std::runtime_error("Failed to compress chunk of " + std::to_string(len) + " bytes, "
+                "LZ4 error: " + std::to_string(compressed_size));
+
+    {
+        auto header = compressed_buffer_.data();
+        WriteUnaligned(header, COMPRESSION_METHOD);
+        // Compressed data size with header
+        WriteUnaligned(header + 1, static_cast<uint32_t>(compressed_size + HEADER_SIZE));
+        // Original data size
+        WriteUnaligned(header + 5, static_cast<uint32_t>(len));
+    }
+
+    WireFormat::WriteFixed(destination_, CityHash128(
+        (const char*)compressed_buffer_.data(), compressed_size + HEADER_SIZE));
+    WireFormat::WriteBytes(destination_, compressed_buffer_.data(), compressed_size + HEADER_SIZE);
+
+    destination_->Flush();
+}
+
+void CompressedOutput::PreallocateCompressBuffer(size_t input_size) {
+    const auto estimated_compressed_buffer_size = LZ4_compressBound(input_size);
+    if (estimated_compressed_buffer_size <= 0)
+        throw std::runtime_error("Failed to estimate compressed buffer size, LZ4 error: " + std::to_string(estimated_compressed_buffer_size));
+
+    compressed_buffer_.resize(estimated_compressed_buffer_size + HEADER_SIZE + EXTRA_COMPRESS_BUFFER_SIZE);
+}
+
 }

clickhouse/base/compressed.h

@@ -1,12 +1,14 @@
 #pragma once
 
-#include "coded.h"
+#include "input.h"
+#include "output.h"
+#include "buffer.h"
 
 namespace clickhouse {
 
 class CompressedInput : public ZeroCopyInput {
 public:
-     CompressedInput(CodedInputStream* input);
+    CompressedInput(InputStream* input);
     ~CompressedInput();
 
 protected:
@@ -15,10 +17,29 @@ class CompressedInput : public ZeroCopyInput {
     bool Decompress();
 
 private:
-    CodedInputStream* const input_;
+    InputStream* const input_;
 
     Buffer data_;
     ArrayInput mem_;
 };
 
+class CompressedOutput : public OutputStream {
+public:
+    CompressedOutput(OutputStream * destination, size_t max_compressed_chunk_size = 0);
+    ~CompressedOutput();
+
+protected:
+    size_t DoWrite(const void* data, size_t len) override;
+    void DoFlush() override;
+
+private:
+    void Compress(const void * data, size_t len);
+    void PreallocateCompressBuffer(size_t input_size);
+
+private:
+    OutputStream * destination_;
+    const size_t max_compressed_chunk_size_;
+    Buffer compressed_buffer_;
+};
+
 }

clickhouse/base/input.cpp

@@ -5,6 +5,21 @@
 
 namespace clickhouse {
 
+bool ZeroCopyInput::Skip(size_t bytes) {
+    while (bytes > 0) {
+        const void* ptr;
+        size_t len = Next(&ptr, bytes);
+
+        if (len == 0) {
+            return false;
+        }
+
+        bytes -= len;
+    }
+
+    return true;
+}
+
 size_t ZeroCopyInput::DoRead(void* buf, size_t len) {
     const void* ptr;
     size_t result = DoNext(&ptr, len);