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Refactor/consolidate legacy Bloom implementation details (#5784) 

Summary:
Refactoring to consolidate implementation details of legacy
Bloom filters. This helps to organize and document some related,
obscure code.

Also added make/cpp var TEST_CACHE_LINE_SIZE so that it's easy to
compile and run unit tests for non-native cache line size. (Fixed a
related test failure in db_properties_test.)
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5784

Test Plan:
make check, including Recently added Bloom schema unit tests
(in ./plain_table_db_test && ./bloom_test), and including with
TEST_CACHE_LINE_SIZE=128U and TEST_CACHE_LINE_SIZE=256U. Tested the
schema tests with temporary fault injection into new implementations.

Some performance testing with modified unit tests suggest a small to moderate
improvement in speed.

Differential Revision: D17381384

Pulled By: pdillinger

fbshipit-source-id: ee42586da996798910fc45ac0b6289147f16d8df
This commit is contained in:
Peter Dillinger 2019-09-16 16:15:18 -07:00 committed by Facebook Github Bot
parent 638d239507
commit 68626249c3
11 changed files with 279 additions and 201 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
Makefile
View File

@ -332,6 +332,11 @@ ifeq ($(USE_FOLLY_DISTRIBUTED_MUTEX),1)
endif
endif
ifdef TEST_CACHE_LINE_SIZE
PLATFORM_CCFLAGS += -DTEST_CACHE_LINE_SIZE=$(TEST_CACHE_LINE_SIZE)
PLATFORM_CXXFLAGS += -DTEST_CACHE_LINE_SIZE=$(TEST_CACHE_LINE_SIZE)
endif
# This (the first rule) must depend on "all".
default: all

12
db/db_properties_test.cc
View File

@ -210,11 +210,10 @@ void VerifySimilar(uint64_t a, uint64_t b, double bias) {
}
}
void VerifyTableProperties(const TableProperties& base_tp,
const TableProperties& new_tp,
double filter_size_bias = 0.1,
double index_size_bias = 0.1,
double data_size_bias = 0.1,
void VerifyTableProperties(
const TableProperties& base_tp, const TableProperties& new_tp,
double filter_size_bias = CACHE_LINE_SIZE >= 256 ? 0.15 : 0.1,
double index_size_bias = 0.1, double data_size_bias = 0.1,
double num_data_blocks_bias = 0.05) {
VerifySimilar(base_tp.data_size, new_tp.data_size, data_size_bias);
VerifySimilar(base_tp.index_size, new_tp.index_size, index_size_bias);
@ -266,7 +265,8 @@ void GetExpectedTableProperties(
// discount 1 byte as value size is not encoded in value delta encoding
(value_delta_encoding ? 1 : 0));
expected_tp->filter_size =
kTableCount * (kKeysPerTable * kBloomBitsPerKey / 8);
kTableCount * ((kKeysPerTable * kBloomBitsPerKey + 7) / 8 +
/*average-ish overhead*/ CACHE_LINE_SIZE / 2);
}
} // anonymous namespace

27
port/port_posix.h
View File

@ -178,22 +178,31 @@ typedef pthread_once_t OnceType;
extern void InitOnce(OnceType* once, void (*initializer)());
#ifndef CACHE_LINE_SIZE
#if defined(__s390__)
#define CACHE_LINE_SIZE 256U
#elif defined(__powerpc__) || defined(__aarch64__)
#define CACHE_LINE_SIZE 128U
#else
#define CACHE_LINE_SIZE 64U
#endif
// To test behavior with non-native cache line size, e.g. for
// Bloom filters, set TEST_CACHE_LINE_SIZE to the desired test size.
// This disables ALIGN_AS to keep it from failing compilation.
#ifdef TEST_CACHE_LINE_SIZE
#define CACHE_LINE_SIZE TEST_CACHE_LINE_SIZE
#define ALIGN_AS(n) /*empty*/
#else
#if defined(__s390__)
#define CACHE_LINE_SIZE 256U
#elif defined(__powerpc__) || defined(__aarch64__)
#define CACHE_LINE_SIZE 128U
#else
#define CACHE_LINE_SIZE 64U
#endif
#define ALIGN_AS(n) alignas(n)
#endif
#endif
static_assert((CACHE_LINE_SIZE & (CACHE_LINE_SIZE - 1)) == 0,
"Cache line size must be a power of 2 number of bytes");
extern void *cacheline_aligned_alloc(size_t size);
extern void cacheline_aligned_free(void *memblock);
#define ALIGN_AS(n) alignas(n)
#define PREFETCH(addr, rw, locality) __builtin_prefetch(addr, rw, locality)
extern void Crash(const std::string& srcfile, int srcline);

7
table/full_filter_bits_builder.h
View File

@ -20,8 +20,7 @@ class Slice;
class FullFilterBitsBuilder : public FilterBitsBuilder {
public:
explicit FullFilterBitsBuilder(const size_t bits_per_key,
const size_t num_probes);
explicit FullFilterBitsBuilder(const int bits_per_key, const int num_probes);
// No Copy allowed
FullFilterBitsBuilder(const FullFilterBitsBuilder&) = delete;
@ -56,8 +55,8 @@ class FullFilterBitsBuilder : public FilterBitsBuilder {
private:
friend class FullFilterBlockTest_DuplicateEntries_Test;
size_t bits_per_key_;
size_t num_probes_;
int bits_per_key_;
int num_probes_;
std::vector<uint32_t> hash_entries_;
// Get totalbits that optimized for cpu cache line

6
table/plain/plain_table_bloom.cc
View File

@ -33,9 +33,9 @@ uint32_t GetTotalBitsForLocality(uint32_t total_bits) {
PlainTableBloomV1::PlainTableBloomV1(uint32_t num_probes)
: kTotalBits(0), kNumBlocks(0), kNumProbes(num_probes), data_(nullptr) {}
void PlainTableBloomV1::SetRawData(unsigned char* raw_data, uint32_t total_bits,
void PlainTableBloomV1::SetRawData(char* raw_data, uint32_t total_bits,
uint32_t num_blocks) {
data_ = reinterpret_cast<uint8_t*>(raw_data);
data_ = raw_data;
kTotalBits = total_bits;
kNumBlocks = num_blocks;
}
@ -63,7 +63,7 @@ void PlainTableBloomV1::SetTotalBits(Allocator* allocator,
if (kNumBlocks > 0 && cache_line_offset > 0) {
raw += CACHE_LINE_SIZE - cache_line_offset;
}
data_ = reinterpret_cast<uint8_t*>(raw);
data_ = raw;
}
void BloomBlockBuilder::AddKeysHashes(const std::vector<uint32_t>& keys_hashes) {

66
table/plain/plain_table_bloom.h
View File

@ -10,8 +10,11 @@
#include "rocksdb/slice.h"
#include "port/port.h"
#include "util/bloom_impl.h"
#include "util/hash.h"
#include "third-party/folly/folly/ConstexprMath.h"
#include <memory>
namespace rocksdb {
@ -50,12 +53,9 @@ class PlainTableBloomV1 {
uint32_t GetNumBlocks() const { return kNumBlocks; }
Slice GetRawData() const {
return Slice(reinterpret_cast<char*>(data_), GetTotalBits() / 8);
}
Slice GetRawData() const { return Slice(data_, GetTotalBits() / 8); }
void SetRawData(unsigned char* raw_data, uint32_t total_bits,
uint32_t num_blocks = 0);
void SetRawData(char* raw_data, uint32_t total_bits, uint32_t num_blocks = 0);
uint32_t GetTotalBits() const { return kTotalBits; }
@ -66,7 +66,10 @@ class PlainTableBloomV1 {
uint32_t kNumBlocks;
const uint32_t kNumProbes;
uint8_t* data_;
char* data_;
static constexpr int LOG2_CACHE_LINE_SIZE =
folly::constexpr_log2(CACHE_LINE_SIZE);
};
#if defined(_MSC_VER)
@ -76,8 +79,9 @@ class PlainTableBloomV1 {
#endif
inline void PlainTableBloomV1::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);
uint32_t ignored;
LegacyLocalityBloomImpl</*ExtraRotates*/ true>::PrepareHashMayMatch(
h, kNumBlocks, data_, &ignored, LOG2_CACHE_LINE_SIZE);
}
}
#if defined(_MSC_VER)
@ -86,54 +90,22 @@ inline void PlainTableBloomV1::Prefetch(uint32_t h) {
inline bool PlainTableBloomV1::MayContainHash(uint32_t h) const {
assert(IsInitialized());
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));
if ((data_[bitpos / 8] & (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;
}
return LegacyLocalityBloomImpl<true>::HashMayMatch(
h, kNumBlocks, kNumProbes, data_, LOG2_CACHE_LINE_SIZE);
} else {
for (uint32_t i = 0; i < kNumProbes; ++i) {
const uint32_t bitpos = h % kTotalBits;
if ((data_[bitpos / 8] & (1 << (bitpos % 8))) == 0) {
return false;
return LegacyNoLocalityBloomImpl::HashMayMatch(h, kTotalBits, kNumProbes,
data_);
}
h += delta;
}
}
return true;
}
inline void PlainTableBloomV1::AddHash(uint32_t h) {
assert(IsInitialized());
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));
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;
}
LegacyLocalityBloomImpl<true>::AddHash(h, kNumBlocks, kNumProbes, data_,
LOG2_CACHE_LINE_SIZE);
} else {
for (uint32_t i = 0; i < kNumProbes; ++i) {
const uint32_t bitpos = h % kTotalBits;
data_[bitpos / 8] |= (1 << (bitpos % 8));
h += delta;
}
LegacyNoLocalityBloomImpl::AddHash(h, kTotalBits, kNumProbes, data_);
}
}

7
table/plain/plain_table_reader.cc
View File

@ -367,10 +367,9 @@ Status PlainTableReader::PopulateIndex(TableProperties* props,
}
}
// cast away const qualifier, because bloom_ won't be changed
bloom_.SetRawData(
const_cast<unsigned char*>(
reinterpret_cast<const unsigned char*>(bloom_block->data())),
static_cast<uint32_t>(bloom_block->size()) * 8, num_blocks);
bloom_.SetRawData(const_cast<char*>(bloom_block->data()),
static_cast<uint32_t>(bloom_block->size()) * 8,
num_blocks);
} else {
// Index in file but no bloom in file. Disable bloom filter in this case.
enable_bloom_ = false;

28
third-party/folly/folly/ConstexprMath.h vendored
View File

@ -14,4 +14,32 @@ template <typename T, typename... Ts>
constexpr T constexpr_max(T a, T b, Ts... ts) {
return b < a ? constexpr_max(a, ts...) : constexpr_max(b, ts...);
}
namespace detail {
template <typename T>
constexpr T constexpr_log2_(T a, T e) {
return e == T(1) ? a : constexpr_log2_(a + T(1), e / T(2));
}
template <typename T>
constexpr T constexpr_log2_ceil_(T l2, T t) {
return l2 + T(T(1) << l2 < t ? 1 : 0);
}
template <typename T>
constexpr T constexpr_square_(T t) {
return t * t;
}
} // namespace detail
template <typename T>
constexpr T constexpr_log2(T t) {
return detail::constexpr_log2_(T(0), t);
}
template <typename T>
constexpr T constexpr_log2_ceil(T t) {
return detail::constexpr_log2_ceil_(constexpr_log2(t), t);
}
} // namespace folly

175
util/bloom.cc
View File

@ -13,19 +13,22 @@
#include "table/block_based/block_based_filter_block.h"
#include "table/block_based/full_filter_block.h"
#include "table/full_filter_bits_builder.h"
#include "third-party/folly/folly/ConstexprMath.h"
#include "util/bloom_impl.h"
#include "util/coding.h"
#include "util/hash.h"
namespace rocksdb {
typedef LegacyLocalityBloomImpl</*ExtraRotates*/ false> LegacyFullFilterImpl;
class BlockBasedFilterBlockBuilder;
class FullFilterBlockBuilder;
FullFilterBitsBuilder::FullFilterBitsBuilder(const size_t bits_per_key,
const size_t num_probes)
FullFilterBitsBuilder::FullFilterBitsBuilder(const int bits_per_key,
const int num_probes)
: bits_per_key_(bits_per_key), num_probes_(num_probes) {
assert(bits_per_key_);
}
}
FullFilterBitsBuilder::~FullFilterBitsBuilder() {}
@ -74,7 +77,7 @@ uint32_t FullFilterBitsBuilder::CalculateSpace(const int num_entry,
uint32_t* num_lines) {
assert(bits_per_key_);
if (num_entry != 0) {
uint32_t total_bits_tmp = num_entry * static_cast<uint32_t>(bits_per_key_);
uint32_t total_bits_tmp = static_cast<uint32_t>(num_entry * bits_per_key_);
*total_bits = GetTotalBitsForLocality(total_bits_tmp);
*num_lines = *total_bits / (CACHE_LINE_SIZE * 8);
@ -124,24 +127,15 @@ inline void FullFilterBitsBuilder::AddHash(uint32_t h, char* data,
#endif
assert(num_lines > 0 && total_bits > 0);
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
uint32_t b = (h % num_lines) * (CACHE_LINE_SIZE * 8);
for (uint32_t i = 0; i < num_probes_; ++i) {
// Since CACHE_LINE_SIZE is defined as 2^n, this line will be optimized
// to a simple operation by compiler.
const uint32_t bitpos = b + (h % (CACHE_LINE_SIZE * 8));
data[bitpos / 8] |= (1 << (bitpos % 8));
h += delta;
}
LegacyFullFilterImpl::AddHash(h, num_lines, num_probes_, data,
folly::constexpr_log2(CACHE_LINE_SIZE));
}
namespace {
class FullFilterBitsReader : public FilterBitsReader {
public:
explicit FullFilterBitsReader(const Slice& contents)
: data_(const_cast<char*>(contents.data())),
: data_(contents.data()),
data_len_(static_cast<uint32_t>(contents.size())),
num_probes_(0),
num_lines_(0),
@ -177,16 +171,23 @@ class FullFilterBitsReader : public FilterBitsReader {
~FullFilterBitsReader() override {}
bool MayMatch(const Slice& entry) override {
// "contents" contains the data built by a preceding call to
// FilterBitsBuilder::Finish. MayMatch must return true if the key was
// passed to FilterBitsBuilder::AddKey. This method may return true or false
// if the key was not on the list, but it should aim to return false with a
// high probability.
bool MayMatch(const Slice& key) override {
if (data_len_ <= 5) { // remain same with original filter
return false;
}
// Other Error params, including a broken filter, regarded as match
if (num_probes_ == 0 || num_lines_ == 0) return true;
uint32_t hash = BloomHash(entry);
uint32_t bit_offset;
FilterPrepare(hash, Slice(data_, data_len_), num_lines_, &bit_offset);
return HashMayMatch(hash, Slice(data_, data_len_), num_probes_, bit_offset);
uint32_t hash = BloomHash(key);
uint32_t byte_offset;
LegacyFullFilterImpl::PrepareHashMayMatch(
hash, num_lines_, data_, /*out*/ &byte_offset, log2_cache_line_size_);
return LegacyFullFilterImpl::HashMayMatchPrepared(
hash, num_probes_, data_ + byte_offset, log2_cache_line_size_);
}
virtual void MayMatch(int num_keys, Slice** keys, bool* may_match) override {
@ -202,16 +203,18 @@ class FullFilterBitsReader : public FilterBitsReader {
// Other Error params, including a broken filter, regarded as match
if (num_probes_ == 0 || num_lines_ == 0) return;
uint32_t hashes[MultiGetContext::MAX_BATCH_SIZE];
uint32_t bit_offsets[MultiGetContext::MAX_BATCH_SIZE];
uint32_t byte_offsets[MultiGetContext::MAX_BATCH_SIZE];
for (int i = 0; i < num_keys; ++i) {
hashes[i] = BloomHash(*keys[i]);
FilterPrepare(hashes[i], Slice(data_, data_len_), num_lines_,
&bit_offsets[i]);
LegacyFullFilterImpl::PrepareHashMayMatch(hashes[i], num_lines_, data_,
/*out*/ &byte_offsets[i],
log2_cache_line_size_);
}
for (int i = 0; i < num_keys; ++i) {
if (!HashMayMatch(hashes[i], Slice(data_, data_len_), num_probes_,
bit_offsets[i])) {
if (!LegacyFullFilterImpl::HashMayMatchPrepared(hashes[i], num_probes_,
data_ + byte_offsets[i],
log2_cache_line_size_)) {
may_match[i] = false;
}
}
@ -219,38 +222,19 @@ class FullFilterBitsReader : public FilterBitsReader {
private:
// Filter meta data
char* data_;
const char* data_;
uint32_t data_len_;
size_t num_probes_;
int num_probes_;
uint32_t num_lines_;
uint32_t log2_cache_line_size_;
// Get num_probes, and num_lines from filter
// If filter format broken, set both to 0.
void GetFilterMeta(const Slice& filter, size_t* num_probes,
uint32_t* num_lines);
// "filter" contains the data appended by a preceding call to
// FilterBitsBuilder::Finish. This method must return true if the key was
// passed to FilterBitsBuilder::AddKey. This method may return true or false
// if the key was not on the list, but it should aim to return false with a
// high probability.
//
// hash: target to be checked
// filter: the whole filter, including meta data bytes
// num_probes: number of probes, read before hand
// num_lines: filter metadata, read before hand
// Before calling this function, need to ensure the input meta data
// is valid.
bool HashMayMatch(const uint32_t& hash, const Slice& filter,
const size_t& num_probes, const uint32_t& bit_offset);
void FilterPrepare(const uint32_t& hash, const Slice& filter,
const uint32_t& num_lines, uint32_t* bit_offset);
void GetFilterMeta(const Slice& filter, int* num_probes, uint32_t* num_lines);
};
void FullFilterBitsReader::GetFilterMeta(const Slice& filter,
size_t* num_probes, uint32_t* num_lines) {
void FullFilterBitsReader::GetFilterMeta(const Slice& filter, int* num_probes,
uint32_t* num_lines) {
uint32_t len = static_cast<uint32_t>(filter.size());
if (len <= 5) {
// filter is empty or broken
@ -263,54 +247,6 @@ void FullFilterBitsReader::GetFilterMeta(const Slice& filter,
*num_lines = DecodeFixed32(filter.data() + len - 4);
}
void FullFilterBitsReader::FilterPrepare(const uint32_t& hash,
const Slice& filter,
const uint32_t& num_lines,
uint32_t* bit_offset) {
uint32_t len = static_cast<uint32_t>(filter.size());
if (len <= 5) return; // remain the same with original filter
// It is ensured the params are valid before calling it
assert(num_lines != 0 && (len - 5) % num_lines == 0);
uint32_t h = hash;
// Left shift by an extra 3 to convert bytes to bits
uint32_t b = (h % num_lines) << (log2_cache_line_size_ + 3);
PREFETCH(&filter.data()[b / 8], 0 /* rw */, 1 /* locality */);
PREFETCH(&filter.data()[b / 8 + (1 << log2_cache_line_size_) - 1],
0 /* rw */, 1 /* locality */);
*bit_offset = b;
}
bool FullFilterBitsReader::HashMayMatch(const uint32_t& hash,
const Slice& filter,
const size_t& num_probes,
const uint32_t& bit_offset) {
uint32_t len = static_cast<uint32_t>(filter.size());
if (len <= 5) return false; // remain the same with original filter
// It is ensured the params are valid before calling it
assert(num_probes != 0);
const char* data = filter.data();
uint32_t h = hash;
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
for (uint32_t i = 0; i < num_probes; ++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 =
bit_offset + (h & ((1 << (log2_cache_line_size_ + 3)) - 1));
if (((data[bitpos / 8]) & (1 << (bitpos % 8))) == 0) {
return false;
}
h += delta;
}
return true;
}
// An implementation of filter policy
class BloomFilterPolicy : public FilterPolicy {
public:
@ -326,56 +262,45 @@ class BloomFilterPolicy : public FilterPolicy {
void CreateFilter(const Slice* keys, int n, std::string* dst) const override {
// Compute bloom filter size (in both bits and bytes)
size_t bits = n * bits_per_key_;
uint32_t bits = static_cast<uint32_t>(n * bits_per_key_);
// For small n, we can see a very high false positive rate. Fix it
// by enforcing a minimum bloom filter length.
if (bits < 64) bits = 64;
size_t bytes = (bits + 7) / 8;
uint32_t bytes = (bits + 7) / 8;
bits = bytes * 8;
const size_t init_size = dst->size();
dst->resize(init_size + bytes, 0);
dst->push_back(static_cast<char>(num_probes_)); // Remember # of probes
char* array = &(*dst)[init_size];
for (size_t i = 0; i < static_cast<size_t>(n); i++) {
// Use double-hashing to generate a sequence of hash values.
// See analysis in [Kirsch,Mitzenmacher 2006].
uint32_t h = hash_func_(keys[i]);
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
for (size_t j = 0; j < num_probes_; j++) {
const uint32_t bitpos = h % bits;
array[bitpos/8] |= (1 << (bitpos % 8));
h += delta;
}
for (int i = 0; i < n; i++) {
LegacyNoLocalityBloomImpl::AddHash(hash_func_(keys[i]), bits, num_probes_,
array);
}
}
bool KeyMayMatch(const Slice& key, const Slice& bloom_filter) const override {
const size_t len = bloom_filter.size();
if (len < 2) return false;
if (len < 2 || len > 0xffffffffU) {
return false;
}
const char* array = bloom_filter.data();
const size_t bits = (len - 1) * 8;
const uint32_t bits = static_cast<uint32_t>(len - 1) * 8;
// Use the encoded k so that we can read filters generated by
// bloom filters created using different parameters.
const size_t k = array[len-1];
const int k = static_cast<uint8_t>(array[len - 1]);
if (k > 30) {
// Reserved for potentially new encodings for short bloom filters.
// Consider it a match.
return true;
}
uint32_t h = hash_func_(key);
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
for (size_t j = 0; j < k; j++) {
const uint32_t bitpos = h % bits;
if ((array[bitpos/8] & (1 << (bitpos % 8))) == 0) return false;
h += delta;
}
return true;
// NB: using k not num_probes_
return LegacyNoLocalityBloomImpl::HashMayMatch(hash_func_(key), bits, k,
array);
}
FilterBitsBuilder* GetFilterBitsBuilder() const override {
@ -394,15 +319,15 @@ class BloomFilterPolicy : public FilterPolicy {
bool UseBlockBasedBuilder() { return use_block_based_builder_; }
private:
size_t bits_per_key_;
size_t num_probes_;
int bits_per_key_;
int num_probes_;
uint32_t (*hash_func_)(const Slice& key);
const bool use_block_based_builder_;
void initialize() {
// We intentionally round down to reduce probing cost a little bit
num_probes_ = static_cast<size_t>(bits_per_key_ * 0.69); // 0.69 =~ ln(2)
num_probes_ = static_cast<int>(bits_per_key_ * 0.69); // 0.69 =~ ln(2)
if (num_probes_ < 1) num_probes_ = 1;
if (num_probes_ > 30) num_probes_ = 30;
}

140
util/bloom_impl.h Normal file
View File

@ -0,0 +1,140 @@
// Copyright (c) 2019-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).
//
// Implementation details of various Bloom filter implementations used in
// RocksDB. (DynamicBloom is in a separate file for now because it
// supports concurrent write.)
#pragma once
#include <stddef.h>
#include <stdint.h>
#include "rocksdb/slice.h"
namespace rocksdb {
// A legacy Bloom filter implementation with no locality of probes (slow).
// It uses double hashing to generate a sequence of hash values.
// Asymptotic analysis is in [Kirsch,Mitzenmacher 2006], but known to have
// subtle accuracy flaws for practical sizes [Dillinger,Manolios 2004].
//
// DO NOT REUSE - faster and more predictably accurate implementations
// are available at
// https://github.com/pdillinger/wormhashing/blob/master/bloom_simulation_tests/foo.cc
// See e.g. RocksDB DynamicBloom.
//
class LegacyNoLocalityBloomImpl {
public:
static inline void AddHash(uint32_t h, uint32_t total_bits,
int num_probes, char *data) {
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
for (int i = 0; i < num_probes; i++) {
const uint32_t bitpos = h % total_bits;
data[bitpos/8] |= (1 << (bitpos % 8));
h += delta;
}
}
static inline bool HashMayMatch(uint32_t h, uint32_t total_bits,
int num_probes, const char *data) {
const uint32_t delta = (h >> 17) | (h << 15); // Rotate right 17 bits
for (int i = 0; i < num_probes; i++) {
const uint32_t bitpos = h % total_bits;
if ((data[bitpos/8] & (1 << (bitpos % 8))) == 0) {
return false;
}
h += delta;
}
return true;
}
};
// A legacy Bloom filter implementation with probes local to a single
// cache line (fast). Because SST files might be transported between
// platforms, the cache line size is a parameter rather than hard coded.
// (But if specified as a constant parameter, an optimizing compiler
// should take advantage of that.)
//
// When ExtraRotates is false, this implementation is notably deficient in
// accuracy. Specifically, it uses double hashing with a 1/512 chance of the
// increment being zero (when cache line size is 512 bits). Thus, there's a
// 1/512 chance of probing only one index, which we'd expect to incur about
// a 1/2 * 1/512 or absolute 0.1% FP rate penalty. More detail at
// https://github.com/facebook/rocksdb/issues/4120
//
// DO NOT REUSE - faster and more predictably accurate implementations
// are available at
// https://github.com/pdillinger/wormhashing/blob/master/bloom_simulation_tests/foo.cc
// See e.g. RocksDB DynamicBloom.
//
template <bool ExtraRotates>
class LegacyLocalityBloomImpl {
private:
static inline uint32_t GetLine(uint32_t h, uint32_t num_lines) {
uint32_t offset_h = ExtraRotates ? (h >> 11) | (h << 21) : h;
return offset_h % num_lines;
}
public:
static inline void AddHash(uint32_t h, uint32_t num_lines,
int num_probes, char *data,
int log2_cache_line_bytes) {
const int log2_cache_line_bits = log2_cache_line_bytes + 3;
char *data_at_offset =
data + (GetLine(h, num_lines) << log2_cache_line_bytes);
const uint32_t delta = (h >> 17) | (h << 15);
for (int i = 0; i < num_probes; ++i) {
// Mask to bit-within-cache-line address
const uint32_t bitpos = h & ((1 << log2_cache_line_bits) - 1);
data_at_offset[bitpos / 8] |= (1 << (bitpos % 8));
if (ExtraRotates) {
h = (h >> log2_cache_line_bits) | (h << (32 - log2_cache_line_bits));
}
h += delta;
}
}
static inline void PrepareHashMayMatch(uint32_t h, uint32_t num_lines,
const char *data,
uint32_t /*out*/*byte_offset,
int log2_cache_line_bytes) {
uint32_t b = GetLine(h, num_lines) << log2_cache_line_bytes;
PREFETCH(data + b, 0 /* rw */, 1 /* locality */);
PREFETCH(data + b + ((1 << log2_cache_line_bytes) - 1),
0 /* rw */, 1 /* locality */);
*byte_offset = b;
}
static inline bool HashMayMatch(uint32_t h, uint32_t num_lines,
int num_probes, const char *data,
int log2_cache_line_bytes) {
uint32_t b = GetLine(h, num_lines) << log2_cache_line_bytes;
return HashMayMatchPrepared(h, num_probes,
data + b, log2_cache_line_bytes);
}
static inline bool HashMayMatchPrepared(uint32_t h, int num_probes,
const char *data_at_offset,
int log2_cache_line_bytes) {
const int log2_cache_line_bits = log2_cache_line_bytes + 3;
const uint32_t delta = (h >> 17) | (h << 15);
for (int i = 0; i < num_probes; ++i) {
// Mask to bit-within-cache-line address
const uint32_t bitpos = h & ((1 << log2_cache_line_bits) - 1);
if (((data_at_offset[bitpos / 8]) & (1 << (bitpos % 8))) == 0) {
return false;
}
if (ExtraRotates) {
h = (h >> log2_cache_line_bits) | (h << (32 - log2_cache_line_bits));
}
h += delta;
}
return true;
}
};
} // namespace rocksdb

3
util/bloom_test.cc
View File

@ -352,7 +352,8 @@ TEST_F(FullBloomTest, FullVaryingLengths) {
}
Build();
ASSERT_LE(FilterSize(), (size_t)((length * 10 / 8) + CACHE_LINE_SIZE * 2 + 5)) << length;
ASSERT_LE(FilterSize(),
(size_t)((length * 10 / 8) + CACHE_LINE_SIZE * 2 + 5));
// All added keys must match
for (int i = 0; i < length; i++) {