mirror of https://github.com/facebook/rocksdb.git
94 lines
3.1 KiB
C++
94 lines
3.1 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#include <string>
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#include <vector>
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#include "rocksdb/slice.h"
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#include "table/block_based/data_block_hash_index.h"
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#include "util/coding.h"
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#include "util/hash.h"
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namespace rocksdb {
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void DataBlockHashIndexBuilder::Add(const Slice& key,
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const size_t restart_index) {
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assert(Valid());
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if (restart_index > kMaxRestartSupportedByHashIndex) {
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valid_ = false;
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return;
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}
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uint32_t hash_value = GetSliceHash(key);
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hash_and_restart_pairs_.emplace_back(hash_value,
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static_cast<uint8_t>(restart_index));
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estimated_num_buckets_ += bucket_per_key_;
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}
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void DataBlockHashIndexBuilder::Finish(std::string& buffer) {
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assert(Valid());
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uint16_t num_buckets = static_cast<uint16_t>(estimated_num_buckets_);
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if (num_buckets == 0) {
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num_buckets = 1; // sanity check
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}
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// The build-in hash cannot well distribute strings when into different
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// buckets when num_buckets is power of two, resulting in high hash
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// collision.
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// We made the num_buckets to be odd to avoid this issue.
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num_buckets |= 1;
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std::vector<uint8_t> buckets(num_buckets, kNoEntry);
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// write the restart_index array
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for (auto& entry : hash_and_restart_pairs_) {
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uint32_t hash_value = entry.first;
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uint8_t restart_index = entry.second;
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uint16_t buck_idx = static_cast<uint16_t>(hash_value % num_buckets);
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if (buckets[buck_idx] == kNoEntry) {
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buckets[buck_idx] = restart_index;
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} else if (buckets[buck_idx] != restart_index) {
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// same bucket cannot store two different restart_index, mark collision
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buckets[buck_idx] = kCollision;
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}
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}
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for (uint8_t restart_index : buckets) {
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buffer.append(
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const_cast<const char*>(reinterpret_cast<char*>(&restart_index)),
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sizeof(restart_index));
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}
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// write NUM_BUCK
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PutFixed16(&buffer, num_buckets);
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assert(buffer.size() <= kMaxBlockSizeSupportedByHashIndex);
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}
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void DataBlockHashIndexBuilder::Reset() {
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estimated_num_buckets_ = 0;
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valid_ = true;
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hash_and_restart_pairs_.clear();
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}
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void DataBlockHashIndex::Initialize(const char* data, uint16_t size,
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uint16_t* map_offset) {
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assert(size >= sizeof(uint16_t)); // NUM_BUCKETS
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num_buckets_ = DecodeFixed16(data + size - sizeof(uint16_t));
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assert(num_buckets_ > 0);
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assert(size > num_buckets_ * sizeof(uint8_t));
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*map_offset = static_cast<uint16_t>(size - sizeof(uint16_t) -
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num_buckets_ * sizeof(uint8_t));
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}
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uint8_t DataBlockHashIndex::Lookup(const char* data, uint32_t map_offset,
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const Slice& key) const {
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uint32_t hash_value = GetSliceHash(key);
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uint16_t idx = static_cast<uint16_t>(hash_value % num_buckets_);
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const char* bucket_table = data + map_offset;
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return static_cast<uint8_t>(*(bucket_table + idx * sizeof(uint8_t)));
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}
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} // namespace rocksdb
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