rocksdb/util/dynamic_bloom.h

// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).

#pragma once

#include <string>

#include "rocksdb/slice.h"

#include "port/port.h"
#include "util/hash.h"

#include <atomic>
#include <memory>

namespace rocksdb {

class Slice;
class Allocator;
class Logger;

// A Bloom filter intended only to be used in memory, never serialized in a way
// that could lead to schema incompatibility. Supports opt-in lock-free
// concurrent access.
class DynamicBloom {
 public:
  // allocator: pass allocator to bloom filter, hence trace the usage of memory
  // total_bits: fixed total bits for the bloom
  // num_probes: number of hash probes for a single key
  // locality:  If positive, optimize for cache line locality, 0 otherwise.
  // hash_func:  customized hash function
  // huge_page_tlb_size:  if >0, try to allocate bloom bytes from huge page TLB
  //                      within this page size. Need to reserve huge pages for
  //                      it to be allocated, like:
  //                         sysctl -w vm.nr_hugepages=20
  //                     See linux doc Documentation/vm/hugetlbpage.txt
  explicit DynamicBloom(Allocator* allocator,
                        uint32_t total_bits, uint32_t locality = 0,
                        uint32_t num_probes = 6,
                        size_t huge_page_tlb_size = 0,
                        Logger* logger = nullptr);

  ~DynamicBloom() {}

  // Assuming single threaded access to this function.
  void Add(const Slice& key);

  // Like Add, but may be called concurrent with other functions.
  void AddConcurrently(const Slice& key);

  // Assuming single threaded access to this function.
  void AddHash(uint32_t hash);

  // Like AddHash, but may be called concurrent with other functions.
  void AddHashConcurrently(uint32_t hash);

  // Multithreaded access to this function is OK
  bool MayContain(const Slice& key) const;

  // Multithreaded access to this function is OK
  bool MayContainHash(uint32_t hash) const;

  void Prefetch(uint32_t h);

  uint32_t GetNumBlocks() const { return kNumBlocks; }

 private:
  uint32_t kTotalBits;
  uint32_t kNumBlocks;
  const uint32_t kNumProbes;

  std::atomic<uint8_t>* data_;

  // or_func(ptr, mask) should effect *ptr |= mask with the appropriate
  // concurrency safety, working with bytes.
  template <typename OrFunc>
  void AddHash(uint32_t hash, const OrFunc& or_func);
};

inline void DynamicBloom::Add(const Slice& key) { AddHash(BloomHash(key)); }

inline void DynamicBloom::AddConcurrently(const Slice& key) {
  AddHashConcurrently(BloomHash(key));
}

inline void DynamicBloom::AddHash(uint32_t hash) {
  AddHash(hash, [](std::atomic<uint8_t>* ptr, uint8_t mask) {
    ptr->store(ptr->load(std::memory_order_relaxed) | mask,
               std::memory_order_relaxed);
  });
}

inline void DynamicBloom::AddHashConcurrently(uint32_t hash) {
  AddHash(hash, [](std::atomic<uint8_t>* ptr, uint8_t mask) {
    // Happens-before between AddHash and MaybeContains is handled by
    // access to versions_->LastSequence(), so all we have to do here is
    // avoid races (so we don't give the compiler a license to mess up
    // our code) and not lose bits.  std::memory_order_relaxed is enough
    // for that.
    if ((mask & ptr->load(std::memory_order_relaxed)) != mask) {
      ptr->fetch_or(mask, std::memory_order_relaxed);
    }
  });
}

inline bool DynamicBloom::MayContain(const Slice& key) const {
  return (MayContainHash(BloomHash(key)));
}

#if defined(_MSC_VER)
#pragma warning(push)
// local variable is initialized but not referenced
#pragma warning(disable : 4189)
#endif
inline void DynamicBloom::Prefetch(uint32_t h) {
  if (kNumBlocks != 0) {
    uint32_t b = ((h >> 11 | (h << 21)) % kNumBlocks) * (CACHE_LINE_SIZE * 8);
    PREFETCH(&(data_[b / 8]), 0, 3);
  }
}
#if defined(_MSC_VER)
#pragma warning(pop)
#endif

inline bool DynamicBloom::MayContainHash(uint32_t h) const {
  const uint32_t delta = (h >> 17) | (h << 15);  // Rotate right 17 bits
  if (kNumBlocks != 0) {
    uint32_t b = ((h >> 11 | (h << 21)) % kNumBlocks) * (CACHE_LINE_SIZE * 8);
    for (uint32_t i = 0; i < kNumProbes; ++i) {
      // Since CACHE_LINE_SIZE is defined as 2^n, this line will be optimized
      //  to a simple and operation by compiler.
      const uint32_t bitpos = b + (h % (CACHE_LINE_SIZE * 8));
      uint8_t byteval = data_[bitpos / 8].load(std::memory_order_relaxed);
      if ((byteval & (1 << (bitpos % 8))) == 0) {
        return false;
      }
      // Rotate h so that we don't reuse the same bytes.
      h = h / (CACHE_LINE_SIZE * 8) +
          (h % (CACHE_LINE_SIZE * 8)) * (0x20000000U / CACHE_LINE_SIZE);
      h += delta;
    }
  } else {
    for (uint32_t i = 0; i < kNumProbes; ++i) {
      const uint32_t bitpos = h % kTotalBits;
      uint8_t byteval = data_[bitpos / 8].load(std::memory_order_relaxed);
      if ((byteval & (1 << (bitpos % 8))) == 0) {
        return false;
      }
      h += delta;
    }
  }
  return true;
}

template <typename OrFunc>
inline void DynamicBloom::AddHash(uint32_t h, const OrFunc& or_func) {
  const uint32_t delta = (h >> 17) | (h << 15);  // Rotate right 17 bits
  if (kNumBlocks != 0) {
    uint32_t b = ((h >> 11 | (h << 21)) % kNumBlocks) * (CACHE_LINE_SIZE * 8);
    for (uint32_t i = 0; i < kNumProbes; ++i) {
      // Since CACHE_LINE_SIZE is defined as 2^n, this line will be optimized
      // to a simple and operation by compiler.
      const uint32_t bitpos = b + (h % (CACHE_LINE_SIZE * 8));
      or_func(&data_[bitpos / 8], (1 << (bitpos % 8)));
      // Rotate h so that we don't reuse the same bytes.
      h = h / (CACHE_LINE_SIZE * 8) +
          (h % (CACHE_LINE_SIZE * 8)) * (0x20000000U / CACHE_LINE_SIZE);
      h += delta;
    }
  } else {
    for (uint32_t i = 0; i < kNumProbes; ++i) {
      const uint32_t bitpos = h % kTotalBits;
      or_func(&data_[bitpos / 8], (1 << (bitpos % 8)));
      h += delta;
    }
  }
}

}  // rocksdb