0d755fff14
Summary: By constraining the probes within cache line(s), we can improve the cache miss rate thus performance. This probably only makes sense for in-memory workload so defaults the option to off. Numbers and comparision can be found in wiki: https://our.intern.facebook.com/intern/wiki/index.php/Ljin/rocksdb_perf/2014_03_17#Bloom_Filter_Study Test Plan: benchmarked this change substantially. Will run make all check as well Reviewers: haobo, igor, dhruba, sdong, yhchiang Reviewed By: haobo CC: leveldb Differential Revision: https://reviews.facebook.net/D17133
102 lines
2.9 KiB
C++
102 lines
2.9 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 <atomic>
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#include <memory>
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namespace rocksdb {
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class Slice;
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class DynamicBloom {
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public:
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// total_bits: fixed total bits for the bloom
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// num_probes: number of hash probes for a single key
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// cl_per_block: block size in cache lines. When this is non-zero, a
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// query/set is done within a block to improve cache locality.
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// hash_func: customized hash function
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explicit DynamicBloom(uint32_t total_bits, uint32_t cl_per_block = 0,
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uint32_t num_probes = 6,
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uint32_t (*hash_func)(const Slice& key) = nullptr);
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~DynamicBloom() {
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delete[] raw_;
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}
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// Assuming single threaded access to this function.
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void Add(const Slice& key);
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// Assuming single threaded access to this function.
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void AddHash(uint32_t hash);
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// Multithreaded access to this function is OK
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bool MayContain(const Slice& key);
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// Multithreaded access to this function is OK
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bool MayContainHash(uint32_t hash);
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private:
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const bool kBlocked;
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const uint32_t kBitsPerBlock;
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const uint32_t kTotalBits;
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const uint32_t kNumBlocks;
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const uint32_t kNumProbes;
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uint32_t (*hash_func_)(const Slice& key);
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unsigned char* data_;
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unsigned char* raw_;
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};
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inline void DynamicBloom::Add(const Slice& key) { AddHash(hash_func_(key)); }
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inline bool DynamicBloom::MayContain(const Slice& key) {
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return (MayContainHash(hash_func_(key)));
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}
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inline bool DynamicBloom::MayContainHash(uint32_t h) {
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const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
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if (kBlocked) {
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uint32_t b = ((h >> 11 | (h << 21)) % kNumBlocks) * kBitsPerBlock;
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for (uint32_t i = 0; i < kNumProbes; ++i) {
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const uint32_t bitpos = b + h % kBitsPerBlock;
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if (((data_[bitpos / 8]) & (1 << (bitpos % 8))) == 0) {
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return false;
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}
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h += delta;
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}
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} else {
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for (uint32_t i = 0; i < kNumProbes; ++i) {
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const uint32_t bitpos = h % kTotalBits;
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if (((data_[bitpos / 8]) & (1 << (bitpos % 8))) == 0) {
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return false;
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}
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h += delta;
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}
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}
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return true;
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}
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inline void DynamicBloom::AddHash(uint32_t h) {
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const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
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if (kBlocked) {
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uint32_t b = ((h >> 11 | (h << 21)) % kNumBlocks) * kBitsPerBlock;
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for (uint32_t i = 0; i < kNumProbes; ++i) {
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const uint32_t bitpos = b + h % kBitsPerBlock;
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data_[bitpos / 8] |= (1 << (bitpos % 8));
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h += delta;
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}
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} else {
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for (uint32_t i = 0; i < kNumProbes; ++i) {
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const uint32_t bitpos = h % kTotalBits;
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data_[bitpos / 8] |= (1 << (bitpos % 8));
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h += delta;
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}
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}
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}
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} // rocksdb
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