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rocksdb/util/ribbon_config.cc

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// Copyright (c) Facebook, Inc. and its affiliates. 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).
#include "util/ribbon_config.h"
namespace ROCKSDB_NAMESPACE::ribbon::detail {
// Each instantiation of this struct is sufficiently unique for configuration
// purposes, and is only instantiated for settings where we support the
// configuration API. An application might only reference one instantiation,
// meaning the rest could be pruned at link time.
template <ConstructionFailureChance kCfc, uint64_t kCoeffBits, bool kUseSmash>
struct BandingConfigHelperData {
static constexpr size_t kKnownSize = 18U;
// Because of complexity in the data, for smaller numbers of slots
// (powers of two up to 2^17), we record known numbers that can be added
// with kCfc chance of construction failure and settings in template
// parameters. Zero means "unsupported (too small) number of slots".
// (GetNumToAdd below will use interpolation for numbers of slots
// between powers of two; double rather than integer values here make
// that more accurate.)
static const std::array<double, kKnownSize> kKnownToAddByPow2;
// For sufficiently large number of slots, doubling the number of
// slots will increase the expected overhead (slots over number added)
// by approximately this constant.
// (This is roughly constant regardless of ConstructionFailureChance and
// smash setting.)
// (Would be a constant if we had partial template specialization for
// static const members.)
static inline double GetFactorPerPow2() {
if (kCoeffBits == 128U) {
return 0.0038;
} else {
assert(kCoeffBits == 64U);
return 0.0083;
}
}
// Overhead factor for 2^(kKnownSize-1) slots
// (Would be a constant if we had partial template specialization for
// static const members.)
static inline double GetFinalKnownFactor() {
return 1.0 * (uint32_t{1} << (kKnownSize - 1)) /
kKnownToAddByPow2[kKnownSize - 1];
}
// GetFinalKnownFactor() - (kKnownSize-1) * GetFactorPerPow2()
// (Would be a constant if we had partial template specialization for
// static const members.)
static inline double GetBaseFactor() {
return GetFinalKnownFactor() - (kKnownSize - 1) * GetFactorPerPow2();
}
// Get overhead factor (slots over number to add) for sufficiently large
// number of slots (by log base 2)
static inline double GetFactorForLarge(double log2_num_slots) {
return GetBaseFactor() + log2_num_slots * GetFactorPerPow2();
}
// For a given power of two number of slots (specified by whole number
// log base 2), implements GetNumToAdd for such limited case, returning
// double for better interpolation in GetNumToAdd and GetNumSlots.
static inline double GetNumToAddForPow2(uint32_t log2_num_slots) {
assert(log2_num_slots <= 32); // help clang-analyze
if (log2_num_slots < kKnownSize) {
return kKnownToAddByPow2[log2_num_slots];
} else {
return 1.0 * (uint64_t{1} << log2_num_slots) /
GetFactorForLarge(1.0 * log2_num_slots);
}
}
};
// Based on data from FindOccupancy in ribbon_test
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn2, 128U, false>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0,
0, // unsupported
252.984,
506.109,
1013.71,
2029.47,
4060.43,
8115.63,
16202.2,
32305.1,
64383.5,
128274,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn2, 128U, /*smash*/ true>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0, // unsupported
126.274,
254.279,
510.27,
1022.24,
2046.02,
4091.99,
8154.98,
16244.3,
32349.7,
64426.6,
128307,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn2, 64U, false>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0, // unsupported
124.94,
249.968,
501.234,
1004.06,
2006.15,
3997.89,
7946.99,
15778.4,
31306.9,
62115.3,
123284,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn2, 64U, /*smash*/ true>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0, // unsupported
62.2683,
126.259,
254.268,
509.975,
1019.98,
2026.16,
4019.75,
7969.8,
15798.2,
31330.3,
62134.2,
123255,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn20, 128U, false>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0,
0, // unsupported
248.851,
499.532,
1001.26,
2003.97,
4005.59,
8000.39,
15966.6,
31828.1,
63447.3,
126506,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn20, 128U, /*smash*/ true>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0, // unsupported
122.637,
250.651,
506.625,
1018.54,
2036.43,
4041.6,
8039.25,
16005,
31869.6,
63492.8,
126537,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn20, 64U, false>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0, // unsupported
120.659,
243.346,
488.168,
976.373,
1948.86,
3875.85,
7704.97,
15312.4,
30395.1,
60321.8,
119813,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn20, 64U, /*smash*/ true>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0, // unsupported
58.6016,
122.619,
250.641,
503.595,
994.165,
1967.36,
3898.17,
7727.21,
15331.5,
30405.8,
60376.2,
119836,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn1000, 128U, false>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0,
0, // unsupported
242.61,
491.887,
983.603,
1968.21,
3926.98,
7833.99,
15629,
31199.9,
62307.8,
123870,
}};
template <>
const std::array<double, 18> BandingConfigHelperData<
kOneIn1000, 128U, /*smash*/ true>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0, // unsupported
117.19,
245.105,
500.748,
1010.67,
1993.4,
3950.01,
7863.31,
15652,
31262.1,
62462.8,
124095,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn1000, 64U, false>::kKnownToAddByPow2{{
0,
0,
0,
0,
0,
0,
0, // unsupported
114,
234.8,
471.498,
940.165,
1874,
3721.5,
7387.5,
14592,
29160,
57745,
115082,
}};
template <>
const std::array<double, 18>
BandingConfigHelperData<kOneIn1000, 64U, /*smash*/ true>::kKnownToAddByPow2{
{
0,
0,
0,
0,
0,
0, // unsupported
53.0434,
117,
245.312,
483.571,
950.251,
1878,
3736.34,
7387.97,
14618,
29142.9,
57838.8,
114932,
}};
// We hide these implementation details from the .h file with explicit
// instantiations below these partial specializations.
template <ConstructionFailureChance kCfc, uint64_t kCoeffBits, bool kUseSmash,
bool kHomogeneous>
uint32_t BandingConfigHelper1MaybeSupported<
kCfc, kCoeffBits, kUseSmash, kHomogeneous,
true /* kIsSupported */>::GetNumToAdd(uint32_t num_slots) {
using Data = detail::BandingConfigHelperData<kCfc, kCoeffBits, kUseSmash>;
if (num_slots == 0) {
return 0;
}
uint32_t num_to_add;
double log2_num_slots = std::log(num_slots) * 1.4426950409;
uint32_t floor_log2 = static_cast<uint32_t>(log2_num_slots);
if (floor_log2 + 1 < Data::kKnownSize) {
double ceil_portion = 1.0 * num_slots / (uint32_t{1} << floor_log2) - 1.0;
// Must be a supported number of slots
assert(Data::kKnownToAddByPow2[floor_log2] > 0.0);
// Weighted average of two nearest known data points
num_to_add = static_cast<uint32_t>(
ceil_portion * Data::kKnownToAddByPow2[floor_log2 + 1] +
(1.0 - ceil_portion) * Data::kKnownToAddByPow2[floor_log2]);
} else {
// Use formula for large values
double factor = Data::GetFactorForLarge(log2_num_slots);
assert(factor >= 1.0);
num_to_add = static_cast<uint32_t>(num_slots / factor);
}
if (kHomogeneous) {
// Even when standard filter construction would succeed, we might
// have loaded things up too much for Homogeneous filter. (Complete
// explanation not known but observed empirically.) This seems to
// correct for that, mostly affecting small filter configurations.
if (num_to_add >= 8) {
num_to_add -= 8;
} else {
assert(false);
}
}
return num_to_add;
}
template <ConstructionFailureChance kCfc, uint64_t kCoeffBits, bool kUseSmash,
bool kHomogeneous>
uint32_t BandingConfigHelper1MaybeSupported<
kCfc, kCoeffBits, kUseSmash, kHomogeneous,
true /* kIsSupported */>::GetNumSlots(uint32_t num_to_add) {
using Data = detail::BandingConfigHelperData<kCfc, kCoeffBits, kUseSmash>;
if (num_to_add == 0) {
return 0;
}
if (kHomogeneous) {
// Reverse of above in GetNumToAdd
num_to_add += 8;
}
double log2_num_to_add = std::log(num_to_add) * 1.4426950409;
uint32_t approx_log2_slots = static_cast<uint32_t>(log2_num_to_add + 0.5);
assert(approx_log2_slots <= 32); // help clang-analyze
double lower_num_to_add = Data::GetNumToAddForPow2(approx_log2_slots);
double upper_num_to_add;
if (approx_log2_slots == 0 || lower_num_to_add == /* unsupported */ 0) {
// Return minimum non-zero slots in standard implementation
return kUseSmash ? kCoeffBits : 2 * kCoeffBits;
} else if (num_to_add < lower_num_to_add) {
upper_num_to_add = lower_num_to_add;
--approx_log2_slots;
lower_num_to_add = Data::GetNumToAddForPow2(approx_log2_slots);
} else {
upper_num_to_add = Data::GetNumToAddForPow2(approx_log2_slots + 1);
}
assert(num_to_add >= lower_num_to_add);
assert(num_to_add < upper_num_to_add);
double upper_portion =
(num_to_add - lower_num_to_add) / (upper_num_to_add - lower_num_to_add);
double lower_num_slots = 1.0 * (uint64_t{1} << approx_log2_slots);
// Interpolation, round up
return static_cast<uint32_t>(upper_portion * lower_num_slots +
lower_num_slots + 0.999999999);
}
// These explicit instantiations enable us to hide most of the
// implementation details from the .h file. (The .h file currently
// needs to determine whether settings are "supported" or not.)
template struct BandingConfigHelper1MaybeSupported<kOneIn2, 128U, /*sm*/ false,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn2, 128U, /*sm*/ true,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn2, 128U, /*sm*/ false,
/*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn2, 128U, /*sm*/ true,
/*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn2, 64U, /*sm*/ false,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn2, 64U, /*sm*/ true,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn2, 64U, /*sm*/ false,
/*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn2, 64U, /*sm*/ true,
/*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn20, 128U, /*sm*/ false,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn20, 128U, /*sm*/ true,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn20, 128U, /*sm*/ false,
/*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn20, 128U, /*sm*/ true,
/*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn20, 64U, /*sm*/ false,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn20, 64U, /*sm*/ true,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn20, 64U, /*sm*/ false,
/*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn20, 64U, /*sm*/ true,
/*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<
kOneIn1000, 128U, /*sm*/ false, /*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<
kOneIn1000, 128U, /*sm*/ true, /*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<
kOneIn1000, 128U, /*sm*/ false, /*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<
kOneIn1000, 128U, /*sm*/ true, /*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<
kOneIn1000, 64U, /*sm*/ false, /*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn1000, 64U, /*sm*/ true,
/*hm*/ false, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<
kOneIn1000, 64U, /*sm*/ false, /*hm*/ true, /*sup*/ true>;
template struct BandingConfigHelper1MaybeSupported<kOneIn1000, 64U, /*sm*/ true,
/*hm*/ true, /*sup*/ true>;
} // namespace ROCKSDB_NAMESPACE::ribbon::detail
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