rocksdb/table/block_based/block_builder.h

//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root 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 <stdint.h>

#include <vector>

#include "rocksdb/slice.h"
#include "rocksdb/table.h"
#include "table/block_based/data_block_hash_index.h"

namespace ROCKSDB_NAMESPACE {

class Statistics;

class BlockBuilder {
 public:
  BlockBuilder(const BlockBuilder&) = delete;
  void operator=(const BlockBuilder&) = delete;

  explicit BlockBuilder(
      int block_restart_interval, bool use_delta_encoding = true,
      bool use_value_delta_encoding = false,
      BlockBasedTableOptions::DataBlockIndexType index_type =
          BlockBasedTableOptions::kDataBlockBinarySearch,
      double data_block_hash_table_util_ratio = 0.75, size_t ts_sz = 0,
      bool persist_user_defined_timestamps = true, bool is_user_key = false,
      bool use_separated_kv_storage = false, Statistics* statistics = nullptr,
      double uniform_cv_threshold = -1.0);

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

  // Swap the contents in BlockBuilder with buffer, then reset the BlockBuilder.
  void SwapAndReset(std::string& buffer);

  // REQUIRES: Finish() has not been called since the last call to Reset().
  // REQUIRES: Unless a range tombstone block, key is larger than any previously
  //           added key
  // DO NOT mix with AddWithLastKey() between Resets. For efficiency, use
  // AddWithLastKey() in contexts where previous added key is already known
  // and delta encoding might be used.
  void Add(const Slice& key, const Slice& value,
           const Slice* const delta_value = nullptr,
           bool skip_delta_encoding = false);

  // A faster version of Add() if the previous key is already known for all
  // Add()s.
  // REQUIRES: Finish() has not been called since the last call to Reset().
  // REQUIRES: Unless a range tombstone block, key is larger than any previously
  //           added key
  // REQUIRES: if AddWithLastKey has been called since last Reset(), last_key
  // is the key from most recent AddWithLastKey. (For convenience, last_key
  // is ignored on first call after creation or Reset().)
  // DO NOT mix with Add() between Resets.
  void AddWithLastKey(const Slice& key, const Slice& value,
                      const Slice& last_key,
                      const Slice* const delta_value = nullptr,
                      bool skip_delta_encoding = false);

  // 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.
  inline size_t CurrentSizeEstimate() const {
    return estimate_ + (data_block_hash_index_builder_.Valid()
                            ? data_block_hash_index_builder_.EstimateSize()
                            : 0);
  }

  // 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(); }

  std::string& MutableBuffer() { return buffer_; }

 private:
  inline void AddWithLastKeyImpl(const Slice& key, const Slice& value,
                                 const Slice& last_key,
                                 const Slice* const delta_value,
                                 bool skip_delta_encoding, size_t buffer_size);

  bool ScanForUniformity() const;

  Slice GetRestartKey(uint32_t index, const char* limit) const;

  inline const Slice MaybeStripTimestampFromKey(std::string* key_buf,
                                                const Slice& key);

  const int block_restart_interval_;
  // TODO(myabandeh): put it into a separate IndexBlockBuilder
  const bool use_delta_encoding_;
  // Refer to BlockIter::DecodeCurrentValue for format of delta encoded values
  const bool use_value_delta_encoding_;
  // Size in bytes for the user-defined timestamp to strip in a user key.
  // This is non-zero if there is user-defined timestamp in the user key and it
  // should not be persisted.
  const size_t strip_ts_sz_;
  // Whether the keys provided to build this block are user keys. If not,
  // the keys are internal keys. This will affect how timestamp stripping is
  // done for the key if `persisted_user_defined_timestamps_` is false and
  // `ts_sz_` is non-zero.
  // The timestamp stripping only applies to the keys added to the block. If the
  // value contains user defined timestamp that needed to be stripped too, such
  // as the `first_internal_key` in an `IndexValue` for an index block, the
  // value part for a range deletion entry, their timestamp should be stripped
  // before calling `BlockBuilder::Add`.
  // Timestamp stripping only applies to data block and index blocks including
  // index block for data blocks, index block for partitioned filter blocks,
  // index block for partitioned index blocks. In summary, this only applies to
  // block whose key are real user keys or internal keys created from user keys.
  const bool is_user_key_;

  std::string buffer_;              // Destination buffer
  std::vector<uint32_t> restarts_;  // Restart points
  size_t estimate_;
  int counter_;    // Number of entries emitted since restart
  bool finished_;  // Has Finish() been called?
  std::string last_key_;
  DataBlockHashIndexBuilder data_block_hash_index_builder_;
  const double uniform_cv_threshold_;
  Statistics* statistics_;

  const bool use_separated_kv_storage_;  // When enabled, keys are stored first,
                                         // followed by values in a separate
                                         // section. Value offset is stored as
                                         // varint only at restart points; for
                                         // other entries, offset is computed
                                         // as prev_offset + prev_length.
  std::string values_buffer_;
#ifndef NDEBUG
  bool add_with_last_key_called_ = false;
#endif
};

}  // namespace ROCKSDB_NAMESPACE