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| -rw-r--r-- | src/rocksdb/db/file_indexer.h | 142 |
1 files changed, 142 insertions, 0 deletions
diff --git a/src/rocksdb/db/file_indexer.h b/src/rocksdb/db/file_indexer.h new file mode 100644 index 00000000..1bef3aab --- /dev/null +++ b/src/rocksdb/db/file_indexer.h @@ -0,0 +1,142 @@ +// 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 <cstdint> +#include <functional> +#include <limits> +#include <vector> +#include "port/port.h" +#include "util/arena.h" +#include "util/autovector.h" + +namespace rocksdb { + +class Comparator; +struct FileMetaData; +struct FdWithKeyRange; +struct FileLevel; + +// The file tree structure in Version is prebuilt and the range of each file +// is known. On Version::Get(), it uses binary search to find a potential file +// and then check if a target key can be found in the file by comparing the key +// to each file's smallest and largest key. The results of these comparisons +// can be reused beyond checking if a key falls into a file's range. +// With some pre-calculated knowledge, each key comparison that has been done +// can serve as a hint to narrow down further searches: if a key compared to +// be smaller than a file's smallest or largest, that comparison can be used +// to find out the right bound of next binary search. Similarly, if a key +// compared to be larger than a file's smallest or largest, it can be utilized +// to find out the left bound of next binary search. +// With these hints: it can greatly reduce the range of binary search, +// especially for bottom levels, given that one file most likely overlaps with +// only N files from level below (where N is max_bytes_for_level_multiplier). +// So on level L, we will only look at ~N files instead of N^L files on the +// naive approach. +class FileIndexer { + public: + explicit FileIndexer(const Comparator* ucmp); + + size_t NumLevelIndex() const; + + size_t LevelIndexSize(size_t level) const; + + // Return a file index range in the next level to search for a key based on + // smallest and largest key comparison for the current file specified by + // level and file_index. When *left_index < *right_index, both index should + // be valid and fit in the vector size. + void GetNextLevelIndex(const size_t level, const size_t file_index, + const int cmp_smallest, const int cmp_largest, + int32_t* left_bound, int32_t* right_bound) const; + + void UpdateIndex(Arena* arena, const size_t num_levels, + std::vector<FileMetaData*>* const files); + + enum { + // MSVC version 1800 still does not have constexpr for ::max() + kLevelMaxIndex = rocksdb::port::kMaxInt32 + }; + + private: + size_t num_levels_; + const Comparator* ucmp_; + + struct IndexUnit { + IndexUnit() + : smallest_lb(0), largest_lb(0), smallest_rb(-1), largest_rb(-1) {} + // During file search, a key is compared against smallest and largest + // from a FileMetaData. It can have 3 possible outcomes: + // (1) key is smaller than smallest, implying it is also smaller than + // larger. Precalculated index based on "smallest < smallest" can + // be used to provide right bound. + // (2) key is in between smallest and largest. + // Precalculated index based on "smallest > greatest" can be used to + // provide left bound. + // Precalculated index based on "largest < smallest" can be used to + // provide right bound. + // (3) key is larger than largest, implying it is also larger than smallest. + // Precalculated index based on "largest > largest" can be used to + // provide left bound. + // + // As a result, we will need to do: + // Compare smallest (<=) and largest keys from upper level file with + // smallest key from lower level to get a right bound. + // Compare smallest (>=) and largest keys from upper level file with + // largest key from lower level to get a left bound. + // + // Example: + // level 1: [50 - 60] + // level 2: [1 - 40], [45 - 55], [58 - 80] + // A key 35, compared to be less than 50, 3rd file on level 2 can be + // skipped according to rule (1). LB = 0, RB = 1. + // A key 53, sits in the middle 50 and 60. 1st file on level 2 can be + // skipped according to rule (2)-a, but the 3rd file cannot be skipped + // because 60 is greater than 58. LB = 1, RB = 2. + // A key 70, compared to be larger than 60. 1st and 2nd file can be skipped + // according to rule (3). LB = 2, RB = 2. + // + // Point to a left most file in a lower level that may contain a key, + // which compares greater than smallest of a FileMetaData (upper level) + int32_t smallest_lb; + // Point to a left most file in a lower level that may contain a key, + // which compares greater than largest of a FileMetaData (upper level) + int32_t largest_lb; + // Point to a right most file in a lower level that may contain a key, + // which compares smaller than smallest of a FileMetaData (upper level) + int32_t smallest_rb; + // Point to a right most file in a lower level that may contain a key, + // which compares smaller than largest of a FileMetaData (upper level) + int32_t largest_rb; + }; + + // Data structure to store IndexUnits in a whole level + struct IndexLevel { + size_t num_index; + IndexUnit* index_units; + + IndexLevel() : num_index(0), index_units(nullptr) {} + }; + + void CalculateLB( + const std::vector<FileMetaData*>& upper_files, + const std::vector<FileMetaData*>& lower_files, IndexLevel* index_level, + std::function<int(const FileMetaData*, const FileMetaData*)> cmp_op, + std::function<void(IndexUnit*, int32_t)> set_index); + + void CalculateRB( + const std::vector<FileMetaData*>& upper_files, + const std::vector<FileMetaData*>& lower_files, IndexLevel* index_level, + std::function<int(const FileMetaData*, const FileMetaData*)> cmp_op, + std::function<void(IndexUnit*, int32_t)> set_index); + + autovector<IndexLevel> next_level_index_; + int32_t* level_rb_; +}; + +} // namespace rocksdb |