fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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140 lines
6.0 KiB
140 lines
6.0 KiB
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include <cstdint>
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#include <functional>
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#include <limits>
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#include <vector>
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#include "util/arena.h"
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#include "util/autovector.h"
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namespace rocksdb {
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class Comparator;
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struct FileMetaData;
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struct FdWithKeyRange;
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struct FileLevel;
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// The file tree structure in Version is prebuilt and the range of each file
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// is known. On Version::Get(), it uses binary search to find a potential file
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// and then check if a target key can be found in the file by comparing the key
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// to each file's smallest and largest key. The results of these comparisions
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// can be reused beyond checking if a key falls into a file's range.
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// With some pre-calculated knowledge, each key comparision that has been done
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// can serve as a hint to narrow down further searches: if a key compared to
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// be smaller than a file's smallest or largest, that comparison can be used
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// to find out the right bound of next binary search. Similarly, if a key
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// compared to be larger than a file's smallest or largest, it can be utilized
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// to find out the left bound of next binary search.
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// With these hints: it can greatly reduce the range of binary search,
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// especially for bottom levels, given that one file most likely overlaps with
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// only N files from level below (where N is max_bytes_for_level_multiplier).
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// So on level L, we will only look at ~N files instead of N^L files on the
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// naive approach.
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class FileIndexer {
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public:
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explicit FileIndexer(const Comparator* ucmp);
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size_t NumLevelIndex() const;
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size_t LevelIndexSize(size_t level) const;
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// Return a file index range in the next level to search for a key based on
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// smallest and largest key comparision for the current file specified by
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// level and file_index. When *left_index < *right_index, both index should
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// be valid and fit in the vector size.
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void GetNextLevelIndex(const size_t level, const size_t file_index,
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const int cmp_smallest, const int cmp_largest,
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int32_t* left_bound, int32_t* right_bound) const;
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void UpdateIndex(Arena* arena, const size_t num_levels,
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std::vector<FileMetaData*>* const files);
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enum {
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kLevelMaxIndex = std::numeric_limits<int32_t>::max()
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};
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private:
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size_t num_levels_;
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const Comparator* ucmp_;
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struct IndexUnit {
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IndexUnit()
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: smallest_lb(0), largest_lb(0), smallest_rb(-1), largest_rb(-1) {}
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// During file search, a key is compared against smallest and largest
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// from a FileMetaData. It can have 3 possible outcomes:
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// (1) key is smaller than smallest, implying it is also smaller than
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// larger. Precalculated index based on "smallest < smallest" can
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// be used to provide right bound.
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// (2) key is in between smallest and largest.
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// Precalculated index based on "smallest > greatest" can be used to
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// provide left bound.
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// Precalculated index based on "largest < smallest" can be used to
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// provide right bound.
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// (3) key is larger than largest, implying it is also larger than smallest.
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// Precalculated index based on "largest > largest" can be used to
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// provide left bound.
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//
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// As a result, we will need to do:
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// Compare smallest (<=) and largest keys from upper level file with
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// smallest key from lower level to get a right bound.
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// Compare smallest (>=) and largest keys from upper level file with
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// largest key from lower level to get a left bound.
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//
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// Example:
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// level 1: [50 - 60]
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// level 2: [1 - 40], [45 - 55], [58 - 80]
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// A key 35, compared to be less than 50, 3rd file on level 2 can be
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// skipped according to rule (1). LB = 0, RB = 1.
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// A key 53, sits in the middle 50 and 60. 1st file on level 2 can be
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// skipped according to rule (2)-a, but the 3rd file cannot be skipped
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// because 60 is greater than 58. LB = 1, RB = 2.
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// A key 70, compared to be larger than 60. 1st and 2nd file can be skipped
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// according to rule (3). LB = 2, RB = 2.
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//
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// Point to a left most file in a lower level that may contain a key,
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// which compares greater than smallest of a FileMetaData (upper level)
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int32_t smallest_lb;
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// Point to a left most file in a lower level that may contain a key,
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// which compares greater than largest of a FileMetaData (upper level)
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int32_t largest_lb;
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// Point to a right most file in a lower level that may contain a key,
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// which compares smaller than smallest of a FileMetaData (upper level)
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int32_t smallest_rb;
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// Point to a right most file in a lower level that may contain a key,
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// which compares smaller than largest of a FileMetaData (upper level)
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int32_t largest_rb;
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};
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// Data structure to store IndexUnits in a whole level
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struct IndexLevel {
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size_t num_index;
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IndexUnit* index_units;
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IndexLevel() : num_index(0), index_units(nullptr) {}
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};
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void CalculateLB(
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const std::vector<FileMetaData*>& upper_files,
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const std::vector<FileMetaData*>& lower_files, IndexLevel* index_level,
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std::function<int(const FileMetaData*, const FileMetaData*)> cmp_op,
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std::function<void(IndexUnit*, int32_t)> set_index);
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void CalculateRB(
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const std::vector<FileMetaData*>& upper_files,
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const std::vector<FileMetaData*>& lower_files, IndexLevel* index_level,
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std::function<int(const FileMetaData*, const FileMetaData*)> cmp_op,
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std::function<void(IndexUnit*, int32_t)> set_index);
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autovector<IndexLevel> next_level_index_;
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int32_t* level_rb_;
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};
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} // namespace rocksdb
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