imay commented on a change in pull request #1646: Support page compression in 
BetaRowset
URL: https://github.com/apache/incubator-doris/pull/1646#discussion_r314316890
 
 

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 File path: be/src/olap/rowset/segment_v2/page_compression.h
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+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#pragma once
+
+#include <cstddef>
+#include <vector>
+
+#include "common/status.h"
+#include "util/slice.h"
+#include "util/faststring.h"
+
+namespace doris {
+
+class BlockCompressionCodec;
+
+namespace segment_v2 {
+
+// Helper to decompress a compressed page.
+// Compressed page is composed of
+// Header | CompressedData
+// Header : uncompressed data length(fixed32)
+// CompressedData: binary
+// Usage: 
+//      Slice compressed_data;
+//      PageDecompressor decompressor(compressed_data, uncomrcodec);
+//      RETURN_IF_ERROR(decompressor.init());
+//      std::string buf;
+//      buf.resize(decompressor.uncompressed_bytes());
+//      RETURN_IF_ERROR(decompress_to(buf.data()));
+class PageDecompressor {
+public:
+    PageDecompressor(const Slice& data, const BlockCompressionCodec* codec)
+        : _data(data), _codec(codec) {
+    }
+
+    // Parse and validate compressed page's header.
+    // Only this funciton is executed successfully, uncompressed_bytes
+    // and decompress_to can be called.
+    // Return error if this page is corrupt.
+    Status init();
+
+    // Get uncompressed size in bytes of this page
+    size_t uncompressed_bytes() const { return _uncompressed_bytes; }
+    
+    // Decmopress compressed data into buf whose capacity must be greater than
+    // uncompressed_bytes()
+    Status decompress_to(void* buf);
+private:
+    Slice _data;
+    const BlockCompressionCodec* _codec;
+    size_t _uncompressed_bytes;
+};
+
+// Helper to build a compress page.
+// Usage:
+//      std::<Slice> raw_data;
 
 Review comment:
   OK

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