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Revision cadc1adffa447f02eb65bd848cf26c13142a74bb authored by sdong on 13 June 2014, 22:54:19 UTC, committed by sdong on 16 June 2014, 23:10:52 UTC 
Refactor: group metadata needed to open an SST file to a separate copyable struct
 
Summary:
We added multiple fields to FileMetaData recently and are planning to add more.
This refactoring separate the minimum information for accessing the file. This object is copyable (FileMetaData is not copyable since the ref counter). I hope this refactoring can enable further improvements:

(1) use it to design a more efficient data structure to speed up read queries.
(2) in the future, when we add information of storage level, we can easily do the encoding, instead of enlarge this structure, which might expand memory work set for file meta data.

The definition is same as current EncodedFileMetaData used in two level iterator, so now the logic in two level iterator is easier to understand.

Test Plan: make all check

Reviewers: haobo, igor, ljin

Reviewed By: ljin

Subscribers: leveldb, dhruba, yhchiang

Differential Revision: https://reviews.facebook.net/D18933
1 parent 4d913cf
Raw File
block_builder.h 
//  Copyright (c) 2013, Facebook, Inc.  All rights reserved.
//  This source code is licensed under the BSD-style license found in the
//  LICENSE file in the root directory of this source tree. An additional grant
//  of patent rights can be found in the PATENTS file in the same directory.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#pragma once
#include <vector>

#include <stdint.h>
#include "rocksdb/slice.h"

namespace rocksdb {

struct Options;
class Comparator;

class BlockBuilder {
 public:
  BlockBuilder(int block_builder, const Comparator* comparator);
  explicit BlockBuilder(const Options& options, const Comparator* comparator);

  // Reset the contents as if the BlockBuilder was just constructed.
  void Reset();

  // REQUIRES: Finish() has not been callled since the last call to Reset().
  // REQUIRES: key is larger than any previously added key
  void Add(const Slice& key, const Slice& value);

  // Finish building the block and return a slice that refers to the
  // block contents.  The returned slice will remain valid for the
  // lifetime of this builder or until Reset() is called.
  Slice Finish();

  // Returns an estimate of the current (uncompressed) size of the block
  // we are building.
  size_t CurrentSizeEstimate() const;

  // Returns an estimated block size after appending key and value.
  size_t EstimateSizeAfterKV(const Slice& key, const Slice& value) const;

  // Return true iff no entries have been added since the last Reset()
  bool empty() const {
    return buffer_.empty();
  }

 private:
  const int          block_restart_interval_;
  const Comparator*  comparator_;

  std::string           buffer_;    // Destination buffer
  std::vector<uint32_t> restarts_;  // Restart points
  int                   counter_;   // Number of entries emitted since restart
  bool                  finished_;  // Has Finish() been called?
  std::string           last_key_;

  // No copying allowed
  BlockBuilder(const BlockBuilder&);
  void operator=(const BlockBuilder&);
};

}  // namespace rocksdb
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