rocksdb/table/block.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 <stddef.h>
#include <stdint.h>

#include "rocksdb/iterator.h"
#include "rocksdb/options.h"
#include "db/dbformat.h"

namespace rocksdb {

struct BlockContents;
class Comparator;
class BlockIter;
class BlockHashIndex;
class BlockPrefixIndex;

class Block {
 public:
  // Initialize the block with the specified contents.
  explicit Block(const BlockContents& contents);

  ~Block();

  size_t size() const { return size_; }
  const char* data() const { return data_; }
  bool cachable() const { return cachable_; }
  uint32_t NumRestarts() const;
  CompressionType compression_type() const { return compression_type_; }

  // If hash index lookup is enabled and `use_hash_index` is true. This block
  // will do hash lookup for the key prefix.
  //
  // NOTE: for the hash based lookup, if a key prefix doesn't match any key,
  // the iterator will simply be set as "invalid", rather than returning
  // the key that is just pass the target key.
  //
  // If iter is null, return new Iterator
  // If iter is not null, update this one and return it as Iterator*
  //
  // If total_order_seek is true, hash_index_ and prefix_index_ are ignored.
  // This option only applies for index block. For data block, hash_index_
  // and prefix_index_ are null, so this option does not matter.
  Iterator* NewIterator(const Comparator* comparator,
      BlockIter* iter = nullptr, bool total_order_seek = true);
  void SetBlockHashIndex(BlockHashIndex* hash_index);
  void SetBlockPrefixIndex(BlockPrefixIndex* prefix_index);

  // Report an approximation of how much memory has been used.
  size_t ApproximateMemoryUsage() const;

 private:
  const char* data_;
  size_t size_;
  uint32_t restart_offset_;     // Offset in data_ of restart array
  bool owned_;                  // Block owns data_[]
  bool cachable_;
  CompressionType compression_type_;
  std::unique_ptr<BlockHashIndex> hash_index_;
  std::unique_ptr<BlockPrefixIndex> prefix_index_;

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

class BlockIter : public Iterator {
 public:
  BlockIter()
      : comparator_(nullptr),
        data_(nullptr),
        restarts_(0),
        num_restarts_(0),
        current_(0),
        restart_index_(0),
        status_(Status::OK()),
        hash_index_(nullptr),
        prefix_index_(nullptr) {}

  BlockIter(const Comparator* comparator, const char* data, uint32_t restarts,
       uint32_t num_restarts, BlockHashIndex* hash_index,
       BlockPrefixIndex* prefix_index)
      : BlockIter() {
    Initialize(comparator, data, restarts, num_restarts,
        hash_index, prefix_index);
  }

  void Initialize(const Comparator* comparator, const char* data,
      uint32_t restarts, uint32_t num_restarts, BlockHashIndex* hash_index,
      BlockPrefixIndex* prefix_index) {
    assert(data_ == nullptr);           // Ensure it is called only once
    assert(num_restarts > 0);           // Ensure the param is valid

    comparator_ = comparator;
    data_ = data;
    restarts_ = restarts;
    num_restarts_ = num_restarts;
    current_ = restarts_;
    restart_index_ = num_restarts_;
    hash_index_ = hash_index;
    prefix_index_ = prefix_index;
  }

  void SetStatus(Status s) {
    status_ = s;
  }

  virtual bool Valid() const override { return current_ < restarts_; }
  virtual Status status() const override { return status_; }
  virtual Slice key() const override {
    assert(Valid());
    return key_.GetKey();
  }
  virtual Slice value() const override {
    assert(Valid());
    return value_;
  }

  virtual void Next() override;

  virtual void Prev() override;

  virtual void Seek(const Slice& target) override;

  virtual void SeekToFirst() override;

  virtual void SeekToLast() override;

 private:
  const Comparator* comparator_;
  const char* data_;       // underlying block contents
  uint32_t restarts_;      // Offset of restart array (list of fixed32)
  uint32_t num_restarts_;  // Number of uint32_t entries in restart array

  // current_ is offset in data_ of current entry.  >= restarts_ if !Valid
  uint32_t current_;
  uint32_t restart_index_;  // Index of restart block in which current_ falls
  IterKey key_;
  Slice value_;
  Status status_;
  BlockHashIndex* hash_index_;
  BlockPrefixIndex* prefix_index_;

  inline int Compare(const Slice& a, const Slice& b) const {
    return comparator_->Compare(a, b);
  }

  // Return the offset in data_ just past the end of the current entry.
  inline uint32_t NextEntryOffset() const {
    return (value_.data() + value_.size()) - data_;
  }

  uint32_t GetRestartPoint(uint32_t index) {
    assert(index < num_restarts_);
    return DecodeFixed32(data_ + restarts_ + index * sizeof(uint32_t));
  }

  void SeekToRestartPoint(uint32_t index) {
    key_.Clear();
    restart_index_ = index;
    // current_ will be fixed by ParseNextKey();

    // ParseNextKey() starts at the end of value_, so set value_ accordingly
    uint32_t offset = GetRestartPoint(index);
    value_ = Slice(data_ + offset, 0);
  }

  void CorruptionError();

  bool ParseNextKey();

  bool BinarySeek(const Slice& target, uint32_t left, uint32_t right,
                  uint32_t* index);

  int CompareBlockKey(uint32_t block_index, const Slice& target);

  bool BinaryBlockIndexSeek(const Slice& target, uint32_t* block_ids,
                            uint32_t left, uint32_t right,
                            uint32_t* index);

  bool HashSeek(const Slice& target, uint32_t* index);

  bool PrefixSeek(const Slice& target, uint32_t* index);

};

}  // namespace rocksdb