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