rocksdb/db/merge_operator.cc

//  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.
//
/**
 * Back-end implementation details specific to the Merge Operator.
 */

#include "rocksdb/merge_operator.h"

namespace rocksdb {

// The default implementation of PartialMergeMulti, which invokes
// PartialMerge multiple times internally and merges two operands at
// a time.
bool MergeOperator::PartialMergeMulti(const Slice& key,
                                      const std::deque<Slice>& operand_list,
                                      std::string* new_value,
                                      Logger* logger) const {
  assert(operand_list.size() >= 2);
  // Simply loop through the operands
  Slice temp_slice(operand_list[0]);

  for (size_t i = 1; i < operand_list.size(); ++i) {
    auto& operand = operand_list[i];
    std::string temp_value;
    if (!PartialMerge(key, temp_slice, operand, &temp_value, logger)) {
      return false;
    }
    swap(temp_value, *new_value);
    temp_slice = Slice(*new_value);
  }

  // The result will be in *new_value. All merges succeeded.
  return true;
}

// Given a "real" merge from the library, call the user's
// associative merge function one-by-one on each of the operands.
// NOTE: It is assumed that the client's merge-operator will handle any errors.
bool AssociativeMergeOperator::FullMerge(
    const Slice& key,
    const Slice* existing_value,
    const std::deque<std::string>& operand_list,
    std::string* new_value,
    Logger* logger) const {

  // Simply loop through the operands
  Slice temp_existing;
  for (const auto& operand : operand_list) {
    Slice value(operand);
    std::string temp_value;
    if (!Merge(key, existing_value, value, &temp_value, logger)) {
      return false;
    }
    swap(temp_value, *new_value);
    temp_existing = Slice(*new_value);
    existing_value = &temp_existing;
  }

  // The result will be in *new_value. All merges succeeded.
  return true;
}

// Call the user defined simple merge on the operands;
// NOTE: It is assumed that the client's merge-operator will handle any errors.
bool AssociativeMergeOperator::PartialMerge(
    const Slice& key,
    const Slice& left_operand,
    const Slice& right_operand,
    std::string* new_value,
    Logger* logger) const {
  return Merge(key, &left_operand, right_operand, new_value, logger);
}

} // namespace rocksdb