rocksdb/table/block_hash_index.h

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// 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