Speedup codec NONE

src/Compression/CachedCompressedReadBuffer.cpp

@@ -51,7 +51,7 @@ bool CachedCompressedReadBuffer::nextImpl()
         {
             owned_cell->additional_bytes = codec->getAdditionalSizeAtTheEndOfBuffer();
             owned_cell->data.resize(size_decompressed + owned_cell->additional_bytes);
-            decompress(owned_cell->data.data(), size_decompressed, size_compressed_without_checksum);
+            decompressTo(owned_cell->data.data(), size_decompressed, size_compressed_without_checksum);
 
         }
 

src/Compression/CompressedReadBuffer.cpp

@@ -21,7 +21,7 @@ bool CompressedReadBuffer::nextImpl()
     memory.resize(size_decompressed + additional_size_at_the_end_of_buffer);
     working_buffer = Buffer(memory.data(), &memory[size_decompressed]);
 
-    decompress(working_buffer.begin(), size_decompressed, size_compressed_without_checksum);
+    decompress(working_buffer, size_decompressed, size_compressed_without_checksum);
 
     return true;
 }
@@ -48,7 +48,7 @@ size_t CompressedReadBuffer::readBig(char * to, size_t n)
         /// If the decompressed block fits entirely where it needs to be copied.
         if (size_decompressed + additional_size_at_the_end_of_buffer <= n - bytes_read)
         {
-            decompress(to + bytes_read, size_decompressed, size_compressed_without_checksum);
+            decompressTo(to + bytes_read, size_decompressed, size_compressed_without_checksum);
             bytes_read += size_decompressed;
             bytes += size_decompressed;
         }
@@ -63,7 +63,7 @@ size_t CompressedReadBuffer::readBig(char * to, size_t n)
             working_buffer = Buffer(memory.data(), &memory[size_decompressed]);
             pos = working_buffer.begin();
 
-            decompress(working_buffer.begin(), size_decompressed, size_compressed_without_checksum);
+            decompress(working_buffer, size_decompressed, size_compressed_without_checksum);
 
             bytes_read += read(to + bytes_read, n - bytes_read);
             break;

src/Compression/CompressedReadBufferBase.cpp

@@ -184,7 +184,7 @@ size_t CompressedReadBufferBase::readCompressedData(size_t & size_decompressed,
 }
 
 
-void CompressedReadBufferBase::decompress(char * to, size_t size_decompressed, size_t size_compressed_without_checksum)
+static void readHeaderAndGetCodec(const char * compressed_buffer, size_t size_decompressed, CompressionCodecPtr & codec, bool allow_different_codecs)
 {
     ProfileEvents::increment(ProfileEvents::CompressedReadBufferBlocks);
     ProfileEvents::increment(ProfileEvents::CompressedReadBufferBytes, size_decompressed);
@@ -210,11 +210,38 @@ void CompressedReadBufferBase::decompress(char * to, size_t size_decompressed, s
                             ErrorCodes::CANNOT_DECOMPRESS);
         }
     }
+}
 
+
+void CompressedReadBufferBase::decompressTo(char * to, size_t size_decompressed, size_t size_compressed_without_checksum)
+{
+    readHeaderAndGetCodec(compressed_buffer, size_decompressed, codec, allow_different_codecs);
     codec->decompress(compressed_buffer, size_compressed_without_checksum, to);
 }
 
 
+void CompressedReadBufferBase::decompress(BufferBase::Buffer & to, size_t size_decompressed, size_t size_compressed_without_checksum)
+{
+    readHeaderAndGetCodec(compressed_buffer, size_decompressed, codec, allow_different_codecs);
+
+    if (codec->isNone())
+    {
+        /// Shortcut for NONE codec to avoid extra memcpy.
+        /// We doing it by changing the buffer `to` to point to existing uncompressed data.
+
+        UInt8 header_size = ICompressionCodec::getHeaderSize();
+        if (size_compressed_without_checksum < header_size)
+            throw Exception(ErrorCodes::CORRUPTED_DATA,
+                "Can't decompress data: the compressed data size ({}), this should include header size) is less than the header size ({})",
+                    size_compressed_without_checksum, size_t(header_size));
+
+        to = BufferBase::Buffer(compressed_buffer + header_size, compressed_buffer + size_compressed_without_checksum);
+    }
+
+    codec->decompress(compressed_buffer, size_compressed_without_checksum, to.begin());
+}
+
+
 /// 'compressed_in' could be initialized lazily, but before first call of 'readCompressedData'.
 CompressedReadBufferBase::CompressedReadBufferBase(ReadBuffer * in, bool allow_different_codecs_)
     : compressed_in(in), own_compressed_buffer(0), allow_different_codecs(allow_different_codecs_)

src/Compression/CompressedReadBufferBase.h

@@ -3,6 +3,7 @@
 #include <Common/PODArray.h>
 #include <Compression/LZ4_decompress_faster.h>
 #include <Compression/ICompressionCodec.h>
+#include <IO/BufferBase.h>
 
 
 namespace DB
@@ -37,7 +38,12 @@ protected:
     /// Returns number of compressed bytes read.
     size_t readCompressedData(size_t & size_decompressed, size_t & size_compressed_without_checksum, bool always_copy);
 
-    void decompress(char * to, size_t size_decompressed, size_t size_compressed_without_checksum);
+    /// Decompress into memory pointed by `to`
+    void decompressTo(char * to, size_t size_decompressed, size_t size_compressed_without_checksum);
+
+    /// This method can change location of `to` to avoid unnecessary copy if data is uncompressed.
+    /// It is more efficient for compression codec NONE but not suitable if you want to decompress into specific location.
+    void decompress(BufferBase::Buffer & to, size_t size_decompressed, size_t size_compressed_without_checksum);
 
 public:
     /// 'compressed_in' could be initialized lazily, but before first call of 'readCompressedData'.

src/Compression/CompressedReadBufferFromFile.cpp

@@ -31,7 +31,7 @@ bool CompressedReadBufferFromFile::nextImpl()
     memory.resize(size_decompressed + additional_size_at_the_end_of_buffer);
     working_buffer = Buffer(memory.data(), &memory[size_decompressed]);
 
-    decompress(working_buffer.begin(), size_decompressed, size_compressed_without_checksum);
+    decompress(working_buffer, size_decompressed, size_compressed_without_checksum);
 
     return true;
 }
@@ -108,7 +108,7 @@ size_t CompressedReadBufferFromFile::readBig(char * to, size_t n)
         /// If the decompressed block fits entirely where it needs to be copied.
         if (size_decompressed + additional_size_at_the_end_of_buffer <= n - bytes_read)
         {
-            decompress(to + bytes_read, size_decompressed, size_compressed_without_checksum);
+            decompressTo(to + bytes_read, size_decompressed, size_compressed_without_checksum);
             bytes_read += size_decompressed;
             bytes += size_decompressed;
         }
@@ -124,7 +124,7 @@ size_t CompressedReadBufferFromFile::readBig(char * to, size_t n)
             working_buffer = Buffer(memory.data(), &memory[size_decompressed]);
             pos = working_buffer.begin();
 
-            decompress(working_buffer.begin(), size_decompressed, size_compressed_without_checksum);
+            decompress(working_buffer, size_decompressed, size_compressed_without_checksum);
 
             bytes_read += read(to + bytes_read, n - bytes_read);
             break;