mirror of
https://github.com/facebook/rocksdb.git
synced 2024-11-26 16:30:56 +00:00
87 lines
3 KiB
C++
87 lines
3 KiB
C++
// Copyright (c) 2011-present, 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.
|
|
#pragma once
|
|
|
|
#include <string>
|
|
#include <unordered_map>
|
|
|
|
#include "rocksdb/status.h"
|
|
#include "util/arena.h"
|
|
#include "util/murmurhash.h"
|
|
|
|
namespace rocksdb {
|
|
|
|
class Comparator;
|
|
class InternalIterator;
|
|
class Slice;
|
|
class SliceTransform;
|
|
|
|
// Build a hash-based index to speed up the lookup for "index block".
|
|
// BlockHashIndex accepts a key and, if found, returns its restart index within
|
|
// that index block.
|
|
class BlockHashIndex {
|
|
public:
|
|
// Represents a restart index in the index block's restart array.
|
|
struct RestartIndex {
|
|
explicit RestartIndex(uint32_t _first_index, uint32_t _num_blocks = 1)
|
|
: first_index(_first_index), num_blocks(_num_blocks) {}
|
|
|
|
// For a given prefix, what is the restart index for the first data block
|
|
// that contains it.
|
|
uint32_t first_index = 0;
|
|
|
|
// How many data blocks contains this prefix?
|
|
uint32_t num_blocks = 1;
|
|
};
|
|
|
|
// @params own_prefixes indicate if we should take care the memory space for
|
|
// the `key_prefix`
|
|
// passed by Add()
|
|
explicit BlockHashIndex(const SliceTransform* hash_key_extractor,
|
|
bool own_prefixes)
|
|
: hash_key_extractor_(hash_key_extractor), kOwnPrefixes(own_prefixes) {}
|
|
|
|
// Maps a key to its restart first_index.
|
|
// Returns nullptr if the restart first_index is found
|
|
const RestartIndex* GetRestartIndex(const Slice& key);
|
|
|
|
bool Add(const Slice& key_prefix, uint32_t restart_index,
|
|
uint32_t num_blocks);
|
|
|
|
size_t ApproximateMemoryUsage() const {
|
|
return arena_.ApproximateMemoryUsage();
|
|
}
|
|
|
|
private:
|
|
const SliceTransform* hash_key_extractor_;
|
|
std::unordered_map<Slice, RestartIndex, murmur_hash> restart_indices_;
|
|
|
|
Arena arena_;
|
|
bool kOwnPrefixes;
|
|
};
|
|
|
|
// Create hash index by reading from the metadata blocks.
|
|
// @params prefixes: a sequence of prefixes.
|
|
// @params prefix_meta: contains the "metadata" to of the prefixes.
|
|
Status CreateBlockHashIndex(const SliceTransform* hash_key_extractor,
|
|
const Slice& prefixes, const Slice& prefix_meta,
|
|
BlockHashIndex** hash_index);
|
|
|
|
// Create hash index by scanning the entries in index as well as the whole
|
|
// dataset.
|
|
// @params index_iter: an iterator with the pointer to the first entry in a
|
|
// block.
|
|
// @params data_iter: an iterator that can scan all the entries reside in a
|
|
// table.
|
|
// @params num_restarts: used for correctness verification.
|
|
// @params hash_key_extractor: extract the hashable part of a given key.
|
|
// On error, nullptr will be returned.
|
|
BlockHashIndex* CreateBlockHashIndexOnTheFly(
|
|
InternalIterator* index_iter, InternalIterator* data_iter,
|
|
const uint32_t num_restarts, const Comparator* comparator,
|
|
const SliceTransform* hash_key_extractor);
|
|
|
|
} // namespace rocksdb
|