rocksdb/util/ribbon_test.cc

//  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 <cmath>

#include "test_util/testharness.h"
#include "util/bloom_impl.h"
#include "util/coding.h"
#include "util/hash.h"
#include "util/ribbon_impl.h"
#include "util/stop_watch.h"

#ifndef GFLAGS
uint32_t FLAGS_thoroughness = 5;
#else
#include "util/gflags_compat.h"
using GFLAGS_NAMESPACE::ParseCommandLineFlags;
// Using 500 is a good test when you have time to be thorough.
// Default is for general RocksDB regression test runs.
DEFINE_uint32(thoroughness, 5, "iterations per configuration");
#endif  // GFLAGS

template <typename TypesAndSettings>
class RibbonTypeParamTest : public ::testing::Test {};

class RibbonTest : public ::testing::Test {};

namespace {

// Different ways of generating keys for testing

// Generate semi-sequential keys
struct StandardKeyGen {
  StandardKeyGen(const std::string& prefix, uint64_t id)
      : id_(id), str_(prefix) {
    ROCKSDB_NAMESPACE::PutFixed64(&str_, /*placeholder*/ 0);
  }

  // Prefix (only one required)
  StandardKeyGen& operator++() {
    ++id_;
    return *this;
  }

  const std::string& operator*() {
    // Use multiplication to mix things up a little in the key
    ROCKSDB_NAMESPACE::EncodeFixed64(&str_[str_.size() - 8],
                                     id_ * uint64_t{0x1500000001});
    return str_;
  }

  bool operator==(const StandardKeyGen& other) {
    // Same prefix is assumed
    return id_ == other.id_;
  }
  bool operator!=(const StandardKeyGen& other) {
    // Same prefix is assumed
    return id_ != other.id_;
  }

  uint64_t id_;
  std::string str_;
};

// Generate small sequential keys, that can misbehave with sequential seeds
// as in https://github.com/Cyan4973/xxHash/issues/469.
// These keys are only heuristically unique, but that's OK with 64 bits,
// for testing purposes.
struct SmallKeyGen {
  SmallKeyGen(const std::string& prefix, uint64_t id) : id_(id) {
    // Hash the prefix for a heuristically unique offset
    id_ += ROCKSDB_NAMESPACE::GetSliceHash64(prefix);
    ROCKSDB_NAMESPACE::PutFixed64(&str_, id_);
  }

  // Prefix (only one required)
  SmallKeyGen& operator++() {
    ++id_;
    return *this;
  }

  const std::string& operator*() {
    ROCKSDB_NAMESPACE::EncodeFixed64(&str_[str_.size() - 8], id_);
    return str_;
  }

  bool operator==(const SmallKeyGen& other) { return id_ == other.id_; }
  bool operator!=(const SmallKeyGen& other) { return id_ != other.id_; }

  uint64_t id_;
  std::string str_;
};

template <typename KeyGen>
struct Hash32KeyGenWrapper : public KeyGen {
  Hash32KeyGenWrapper(const std::string& prefix, uint64_t id)
      : KeyGen(prefix, id) {}
  uint32_t operator*() {
    auto& key = *static_cast<KeyGen&>(*this);
    // unseeded
    return ROCKSDB_NAMESPACE::GetSliceHash(key);
  }
};

template <typename KeyGen>
struct Hash64KeyGenWrapper : public KeyGen {
  Hash64KeyGenWrapper(const std::string& prefix, uint64_t id)
      : KeyGen(prefix, id) {}
  uint64_t operator*() {
    auto& key = *static_cast<KeyGen&>(*this);
    // unseeded
    return ROCKSDB_NAMESPACE::GetSliceHash64(key);
  }
};

}  // namespace

using ROCKSDB_NAMESPACE::ribbon::ExpectedCollisionFpRate;
using ROCKSDB_NAMESPACE::ribbon::StandardHasher;
using ROCKSDB_NAMESPACE::ribbon::StandardRehasherAdapter;

struct DefaultTypesAndSettings {
  using CoeffRow = ROCKSDB_NAMESPACE::Unsigned128;
  using ResultRow = uint8_t;
  using Index = uint32_t;
  using Hash = uint64_t;
  using Seed = uint32_t;
  using Key = ROCKSDB_NAMESPACE::Slice;
  static constexpr bool kIsFilter = true;
  static constexpr bool kFirstCoeffAlwaysOne = true;
  static constexpr bool kUseSmash = false;
  static constexpr bool kAllowZeroStarts = false;
  static Hash HashFn(const Key& key, uint64_t raw_seed) {
    // This version 0.7.2 preview of XXH3 (a.k.a. XXH3p) function does
    // not pass SmallKeyGen tests below without some seed premixing from
    // StandardHasher. See https://github.com/Cyan4973/xxHash/issues/469
    return ROCKSDB_NAMESPACE::Hash64(key.data(), key.size(), raw_seed);
  }
  // For testing
  using KeyGen = StandardKeyGen;
};

using TypesAndSettings_Coeff128 = DefaultTypesAndSettings;
struct TypesAndSettings_Coeff128Smash : public DefaultTypesAndSettings {
  static constexpr bool kUseSmash = true;
};
struct TypesAndSettings_Coeff64 : public DefaultTypesAndSettings {
  using CoeffRow = uint64_t;
};
struct TypesAndSettings_Coeff64Smash1 : public DefaultTypesAndSettings {
  using CoeffRow = uint64_t;
  static constexpr bool kUseSmash = true;
};
struct TypesAndSettings_Coeff64Smash0 : public TypesAndSettings_Coeff64Smash1 {
  static constexpr bool kFirstCoeffAlwaysOne = false;
};
struct TypesAndSettings_Result16 : public DefaultTypesAndSettings {
  using ResultRow = uint16_t;
};
struct TypesAndSettings_Result32 : public DefaultTypesAndSettings {
  using ResultRow = uint32_t;
};
struct TypesAndSettings_IndexSizeT : public DefaultTypesAndSettings {
  using Index = size_t;
};
struct TypesAndSettings_Hash32 : public DefaultTypesAndSettings {
  using Hash = uint32_t;
  static Hash HashFn(const Key& key, Hash raw_seed) {
    // This MurmurHash1 function does not pass tests below without the
    // seed premixing from StandardHasher. In fact, it needs more than
    // just a multiplication mixer on the ordinal seed.
    return ROCKSDB_NAMESPACE::Hash(key.data(), key.size(), raw_seed);
  }
};
struct TypesAndSettings_Hash32_Result16 : public TypesAndSettings_Hash32 {
  using ResultRow = uint16_t;
};
struct TypesAndSettings_KeyString : public DefaultTypesAndSettings {
  using Key = std::string;
};
struct TypesAndSettings_Seed8 : public DefaultTypesAndSettings {
  // This is not a generally recommended configuration. With the configured
  // hash function, it would fail with SmallKeyGen due to insufficient
  // independence among the seeds.
  using Seed = uint8_t;
};
struct TypesAndSettings_NoAlwaysOne : public DefaultTypesAndSettings {
  static constexpr bool kFirstCoeffAlwaysOne = false;
};
struct TypesAndSettings_AllowZeroStarts : public DefaultTypesAndSettings {
  static constexpr bool kAllowZeroStarts = true;
};
struct TypesAndSettings_Seed64 : public DefaultTypesAndSettings {
  using Seed = uint64_t;
};
struct TypesAndSettings_Rehasher
    : public StandardRehasherAdapter<DefaultTypesAndSettings> {
  using KeyGen = Hash64KeyGenWrapper<StandardKeyGen>;
};
struct TypesAndSettings_Rehasher_Result16 : public TypesAndSettings_Rehasher {
  using ResultRow = uint16_t;
};
struct TypesAndSettings_Rehasher_Result32 : public TypesAndSettings_Rehasher {
  using ResultRow = uint32_t;
};
struct TypesAndSettings_Rehasher_Seed64
    : public StandardRehasherAdapter<TypesAndSettings_Seed64> {
  using KeyGen = Hash64KeyGenWrapper<StandardKeyGen>;
  // Note: 64-bit seed with Rehasher gives slightly better average reseeds
};
struct TypesAndSettings_Rehasher32
    : public StandardRehasherAdapter<TypesAndSettings_Hash32> {
  using KeyGen = Hash32KeyGenWrapper<StandardKeyGen>;
};
struct TypesAndSettings_Rehasher32_Coeff64
    : public TypesAndSettings_Rehasher32 {
  using CoeffRow = uint64_t;
};
struct TypesAndSettings_SmallKeyGen : public DefaultTypesAndSettings {
  // SmallKeyGen stresses the independence of different hash seeds
  using KeyGen = SmallKeyGen;
};
struct TypesAndSettings_Hash32_SmallKeyGen : public TypesAndSettings_Hash32 {
  // SmallKeyGen stresses the independence of different hash seeds
  using KeyGen = SmallKeyGen;
};

using TestTypesAndSettings = ::testing::Types<
    TypesAndSettings_Coeff128, TypesAndSettings_Coeff128Smash,
    TypesAndSettings_Coeff64, TypesAndSettings_Coeff64Smash0,
    TypesAndSettings_Coeff64Smash1, TypesAndSettings_Result16,
    TypesAndSettings_Result32, TypesAndSettings_IndexSizeT,
    TypesAndSettings_Hash32, TypesAndSettings_Hash32_Result16,
    TypesAndSettings_KeyString, TypesAndSettings_Seed8,
    TypesAndSettings_NoAlwaysOne, TypesAndSettings_AllowZeroStarts,
    TypesAndSettings_Seed64, TypesAndSettings_Rehasher,
    TypesAndSettings_Rehasher_Result16, TypesAndSettings_Rehasher_Result32,
    TypesAndSettings_Rehasher_Seed64, TypesAndSettings_Rehasher32,
    TypesAndSettings_Rehasher32_Coeff64, TypesAndSettings_SmallKeyGen,
    TypesAndSettings_Hash32_SmallKeyGen>;
TYPED_TEST_CASE(RibbonTypeParamTest, TestTypesAndSettings);

namespace {

// For testing Poisson-distributed (or similar) statistics, get value for
// `stddevs_allowed` standard deviations above expected mean
// `expected_count`.
// (Poisson approximates Binomial only if probability of a trial being
// in the count is low.)
uint64_t PoissonUpperBound(double expected_count, double stddevs_allowed) {
  return static_cast<uint64_t>(
      expected_count + stddevs_allowed * std::sqrt(expected_count) + 1.0);
}

uint64_t PoissonLowerBound(double expected_count, double stddevs_allowed) {
  return static_cast<uint64_t>(std::max(
      0.0, expected_count - stddevs_allowed * std::sqrt(expected_count)));
}

uint64_t FrequentPoissonUpperBound(double expected_count) {
  // Allow up to 5.0 standard deviations for frequently checked statistics
  return PoissonUpperBound(expected_count, 5.0);
}

uint64_t FrequentPoissonLowerBound(double expected_count) {
  return PoissonLowerBound(expected_count, 5.0);
}

uint64_t InfrequentPoissonUpperBound(double expected_count) {
  // Allow up to 3 standard deviations for infrequently checked statistics
  return PoissonUpperBound(expected_count, 3.0);
}

uint64_t InfrequentPoissonLowerBound(double expected_count) {
  return PoissonLowerBound(expected_count, 3.0);
}

}  // namespace

TYPED_TEST(RibbonTypeParamTest, CompactnessAndBacktrackAndFpRate) {
  IMPORT_RIBBON_TYPES_AND_SETTINGS(TypeParam);
  IMPORT_RIBBON_IMPL_TYPES(TypeParam);
  using KeyGen = typename TypeParam::KeyGen;

  // For testing FP rate etc.
  constexpr Index kNumToCheck = 100000;

  const auto log2_thoroughness =
      static_cast<Hash>(ROCKSDB_NAMESPACE::FloorLog2(FLAGS_thoroughness));

  // With overhead of just 2%, expect ~50% encoding success per
  // seed with ~5k keys on 64-bit ribbon, or ~150k keys on 128-bit ribbon.
  const double kFactor = 1.02;

  uint64_t total_reseeds = 0;
  uint64_t total_single_failures = 0;
  uint64_t total_batch_successes = 0;
  uint64_t total_fp_count = 0;
  uint64_t total_added = 0;

  uint64_t soln_query_nanos = 0;
  uint64_t soln_query_count = 0;
  uint64_t bloom_query_nanos = 0;
  uint64_t isoln_query_nanos = 0;
  uint64_t isoln_query_count = 0;

  // Take different samples if you change thoroughness
  ROCKSDB_NAMESPACE::Random32 rnd(FLAGS_thoroughness);

  for (uint32_t i = 0; i < FLAGS_thoroughness; ++i) {
    uint32_t num_to_add =
        sizeof(CoeffRow) == 16 ? 130000 : TypeParam::kUseSmash ? 5500 : 2500;

    // Use different values between that number and 50% of that number
    num_to_add -= rnd.Uniformish(num_to_add / 2);

    total_added += num_to_add;

    // Most of the time, test the Interleaved solution storage, but when
    // we do we have to make num_slots a multiple of kCoeffBits. So
    // sometimes we want to test without that limitation.
    bool test_interleaved = (i % 7) != 6;

    Index num_slots = static_cast<Index>(num_to_add * kFactor);
    if (test_interleaved) {
      // Round to nearest multiple of kCoeffBits
      num_slots = ((num_slots + kCoeffBits / 2) / kCoeffBits) * kCoeffBits;
      // Re-adjust num_to_add to get as close as possible to kFactor
      num_to_add = static_cast<uint32_t>(num_slots / kFactor);
    }

    std::string prefix;
    ROCKSDB_NAMESPACE::PutFixed32(&prefix, rnd.Next());

    // Batch that must be added
    std::string added_str = prefix + "added";
    KeyGen keys_begin(added_str, 0);
    KeyGen keys_end(added_str, num_to_add);

    // A couple more that will probably be added
    KeyGen one_more(prefix + "more", 1);
    KeyGen two_more(prefix + "more", 2);

    // Batch that may or may not be added
    const Index kBatchSize =
        sizeof(CoeffRow) == 16 ? 300 : TypeParam::kUseSmash ? 20 : 10;
    std::string batch_str = prefix + "batch";
    KeyGen batch_begin(batch_str, 0);
    KeyGen batch_end(batch_str, kBatchSize);

    // Batch never (successfully) added, but used for querying FP rate
    std::string not_str = prefix + "not";
    KeyGen other_keys_begin(not_str, 0);
    KeyGen other_keys_end(not_str, kNumToCheck);

    // Vary bytes for InterleavedSoln to use number of solution columns
    // from 0 to max allowed by ResultRow type (and used by SimpleSoln).
    // Specifically include 0 and max, and otherwise skew toward max.
    uint32_t max_ibytes = static_cast<uint32_t>(sizeof(ResultRow) * num_slots);
    size_t ibytes;
    if (i == 0) {
      ibytes = 0;
    } else if (i == 1) {
      ibytes = max_ibytes;
    } else {
      // Skewed
      ibytes = std::max(rnd.Uniformish(max_ibytes), rnd.Uniformish(max_ibytes));
    }
    std::unique_ptr<char[]> idata(new char[ibytes]);
    InterleavedSoln isoln(idata.get(), ibytes);

    SimpleSoln soln;
    Hasher hasher;
    bool first_single;
    bool second_single;
    bool batch_success;
    {
      Banding banding;
      // Traditional solve for a fixed set.
      ASSERT_TRUE(
          banding.ResetAndFindSeedToSolve(num_slots, keys_begin, keys_end));

      // Now to test backtracking, starting with guaranteed fail. By using
      // the keys that will be used to test FP rate, we are then doing an
      // extra check that after backtracking there are no remnants (e.g. in
      // result side of banding) of these entries.
      Index occupied_count = banding.GetOccupiedCount();
      banding.EnsureBacktrackSize(kNumToCheck);
      EXPECT_FALSE(
          banding.AddRangeOrRollBack(other_keys_begin, other_keys_end));
      EXPECT_EQ(occupied_count, banding.GetOccupiedCount());

      // Check that we still have a good chance of adding a couple more
      // individually
      first_single = banding.Add(*one_more);
      second_single = banding.Add(*two_more);
      Index more_added = (first_single ? 1 : 0) + (second_single ? 1 : 0);
      total_single_failures += 2U - more_added;

      // Or as a batch
      batch_success = banding.AddRangeOrRollBack(batch_begin, batch_end);
      if (batch_success) {
        more_added += kBatchSize;
        ++total_batch_successes;
      }
      EXPECT_LE(banding.GetOccupiedCount(), occupied_count + more_added);

      // Also verify that redundant adds are OK (no effect)
      ASSERT_TRUE(
          banding.AddRange(keys_begin, KeyGen(added_str, num_to_add / 8)));
      EXPECT_LE(banding.GetOccupiedCount(), occupied_count + more_added);

      // Now back-substitution
      soln.BackSubstFrom(banding);
      if (test_interleaved) {
        isoln.BackSubstFrom(banding);
      }

      Seed reseeds = banding.GetOrdinalSeed();
      total_reseeds += reseeds;

      EXPECT_LE(reseeds, 8 + log2_thoroughness);
      if (reseeds > log2_thoroughness + 1) {
        fprintf(
            stderr, "%s high reseeds at %u, %u/%u: %u\n",
            reseeds > log2_thoroughness + 8 ? "ERROR Extremely" : "Somewhat",
            static_cast<unsigned>(i), static_cast<unsigned>(num_to_add),
            static_cast<unsigned>(num_slots), static_cast<unsigned>(reseeds));
      }
      hasher.SetOrdinalSeed(reseeds);
    }
    // soln and hasher now independent of Banding object

    // Verify keys added
    KeyGen cur = keys_begin;
    while (cur != keys_end) {
      ASSERT_TRUE(soln.FilterQuery(*cur, hasher));
      ASSERT_TRUE(!test_interleaved || isoln.FilterQuery(*cur, hasher));
      ++cur;
    }
    // We (maybe) snuck these in!
    if (first_single) {
      ASSERT_TRUE(soln.FilterQuery(*one_more, hasher));
      ASSERT_TRUE(!test_interleaved || isoln.FilterQuery(*one_more, hasher));
    }
    if (second_single) {
      ASSERT_TRUE(soln.FilterQuery(*two_more, hasher));
      ASSERT_TRUE(!test_interleaved || isoln.FilterQuery(*two_more, hasher));
    }
    if (batch_success) {
      cur = batch_begin;
      while (cur != batch_end) {
        ASSERT_TRUE(soln.FilterQuery(*cur, hasher));
        ASSERT_TRUE(!test_interleaved || isoln.FilterQuery(*cur, hasher));
        ++cur;
      }
    }

    // Check FP rate (depends only on number of result bits == solution columns)
    Index fp_count = 0;
    cur = other_keys_begin;
    {
      ROCKSDB_NAMESPACE::StopWatchNano timer(ROCKSDB_NAMESPACE::Env::Default(),
                                             true);
      while (cur != other_keys_end) {
        bool fp = soln.FilterQuery(*cur, hasher);
        fp_count += fp ? 1 : 0;
        ++cur;
      }
      soln_query_nanos += timer.ElapsedNanos();
      soln_query_count += kNumToCheck;
    }
    {
      double expected_fp_count = soln.ExpectedFpRate() * kNumToCheck;
      // For expected FP rate, also include false positives due to collisions
      // in Hash value. (Negligible for 64-bit, can matter for 32-bit.)
      double correction =
          kNumToCheck * ExpectedCollisionFpRate(hasher, num_to_add);
      EXPECT_LE(fp_count,
                FrequentPoissonUpperBound(expected_fp_count + correction));
      EXPECT_GE(fp_count,
                FrequentPoissonLowerBound(expected_fp_count + correction));
    }
    total_fp_count += fp_count;

    // And also check FP rate for isoln
    if (test_interleaved) {
      Index ifp_count = 0;
      cur = other_keys_begin;
      ROCKSDB_NAMESPACE::StopWatchNano timer(ROCKSDB_NAMESPACE::Env::Default(),
                                             true);
      while (cur != other_keys_end) {
        ifp_count += isoln.FilterQuery(*cur, hasher) ? 1 : 0;
        ++cur;
      }
      isoln_query_nanos += timer.ElapsedNanos();
      isoln_query_count += kNumToCheck;
      {
        double expected_fp_count = isoln.ExpectedFpRate() * kNumToCheck;
        // For expected FP rate, also include false positives due to collisions
        // in Hash value. (Negligible for 64-bit, can matter for 32-bit.)
        double correction =
            kNumToCheck * ExpectedCollisionFpRate(hasher, num_to_add);
        EXPECT_LE(ifp_count,
                  FrequentPoissonUpperBound(expected_fp_count + correction));
        EXPECT_GE(ifp_count,
                  FrequentPoissonLowerBound(expected_fp_count + correction));
      }
      // Since the bits used in isoln are a subset of the bits used in soln,
      // it cannot have fewer FPs
      EXPECT_GE(ifp_count, fp_count);
    }

    // And compare to Bloom time, for fun
    if (ibytes >= /* minimum Bloom impl bytes*/ 64) {
      Index bfp_count = 0;
      cur = other_keys_begin;
      ROCKSDB_NAMESPACE::StopWatchNano timer(ROCKSDB_NAMESPACE::Env::Default(),
                                             true);
      while (cur != other_keys_end) {
        uint64_t h = hasher.GetHash(*cur);
        uint32_t h1 = ROCKSDB_NAMESPACE::Lower32of64(h);
        uint32_t h2 = sizeof(Hash) >= 8 ? ROCKSDB_NAMESPACE::Upper32of64(h)
                                        : h1 * 0x9e3779b9;
        bfp_count += ROCKSDB_NAMESPACE::FastLocalBloomImpl::HashMayMatch(
                         h1, h2, static_cast<uint32_t>(ibytes), 6, idata.get())
                         ? 1
                         : 0;
        ++cur;
      }
      bloom_query_nanos += timer.ElapsedNanos();
      // ensure bfp_count is used
      ASSERT_LT(bfp_count, kNumToCheck);
    }
  }

  // "outside" == key not in original set so either negative or false positive
  fprintf(stderr, "Simple      outside query, hot, incl hashing, ns/key: %g\n",
          1.0 * soln_query_nanos / soln_query_count);
  fprintf(stderr, "Interleaved outside query, hot, incl hashing, ns/key: %g\n",
          1.0 * isoln_query_nanos / isoln_query_count);
  fprintf(stderr, "Bloom       outside query, hot, incl hashing, ns/key: %g\n",
          1.0 * bloom_query_nanos / soln_query_count);

  {
    double average_reseeds = 1.0 * total_reseeds / FLAGS_thoroughness;
    fprintf(stderr, "Average re-seeds: %g\n", average_reseeds);
    // Values above were chosen to target around 50% chance of encoding success
    // rate (average of 1.0 re-seeds) or slightly better. But 1.15 is also close
    // enough.
    EXPECT_LE(total_reseeds,
              InfrequentPoissonUpperBound(1.15 * FLAGS_thoroughness));
    // Would use 0.85 here instead of 0.75, but
    // TypesAndSettings_Hash32_SmallKeyGen can "beat the odds" because of
    // sequential keys with a small, cheap hash function. We accept that
    // there are surely inputs that are somewhat bad for this setup, but
    // these somewhat good inputs are probably more likely.
    EXPECT_GE(total_reseeds,
              InfrequentPoissonLowerBound(0.75 * FLAGS_thoroughness));
  }

  {
    uint64_t total_singles = 2 * FLAGS_thoroughness;
    double single_failure_rate = 1.0 * total_single_failures / total_singles;
    fprintf(stderr, "Add'l single, failure rate: %g\n", single_failure_rate);
    // A rough bound (one sided) based on nothing in particular
    double expected_single_failures =
        1.0 * total_singles /
        (sizeof(CoeffRow) == 16 ? 128 : TypeParam::kUseSmash ? 64 : 32);
    EXPECT_LE(total_single_failures,
              InfrequentPoissonUpperBound(expected_single_failures));
  }

  {
    // Counting successes here for Poisson to approximate the Binomial
    // distribution.
    // A rough bound (one sided) based on nothing in particular.
    double expected_batch_successes = 1.0 * FLAGS_thoroughness / 2;
    uint64_t lower_bound =
        InfrequentPoissonLowerBound(expected_batch_successes);
    fprintf(stderr, "Add'l batch, success rate: %g (>= %g)\n",
            1.0 * total_batch_successes / FLAGS_thoroughness,
            1.0 * lower_bound / FLAGS_thoroughness);
    EXPECT_GE(total_batch_successes, lower_bound);
  }

  {
    uint64_t total_checked = uint64_t{kNumToCheck} * FLAGS_thoroughness;
    double expected_total_fp_count =
        total_checked * std::pow(0.5, 8U * sizeof(ResultRow));
    // For expected FP rate, also include false positives due to collisions
    // in Hash value. (Negligible for 64-bit, can matter for 32-bit.)
    double average_added = 1.0 * total_added / FLAGS_thoroughness;
    expected_total_fp_count +=
        total_checked * ExpectedCollisionFpRate(Hasher(), average_added);

    uint64_t upper_bound = InfrequentPoissonUpperBound(expected_total_fp_count);
    uint64_t lower_bound = InfrequentPoissonLowerBound(expected_total_fp_count);
    fprintf(stderr, "Average FP rate: %g (~= %g, <= %g, >= %g)\n",
            1.0 * total_fp_count / total_checked,
            expected_total_fp_count / total_checked,
            1.0 * upper_bound / total_checked,
            1.0 * lower_bound / total_checked);
    EXPECT_LE(total_fp_count, upper_bound);
    EXPECT_GE(total_fp_count, lower_bound);
  }
}

TYPED_TEST(RibbonTypeParamTest, Extremes) {
  IMPORT_RIBBON_TYPES_AND_SETTINGS(TypeParam);
  IMPORT_RIBBON_IMPL_TYPES(TypeParam);
  using KeyGen = typename TypeParam::KeyGen;

  size_t bytes = 128 * 1024;
  std::unique_ptr<char[]> buf(new char[bytes]);
  InterleavedSoln isoln(buf.get(), bytes);
  SimpleSoln soln;
  Hasher hasher;
  Banding banding;

  // ########################################
  // Add zero keys to minimal number of slots
  KeyGen begin_and_end("foo", 123);
  ASSERT_TRUE(banding.ResetAndFindSeedToSolve(
      /*slots*/ kCoeffBits, begin_and_end, begin_and_end, /*first seed*/ 0,
      /* seed mask*/ 0));

  soln.BackSubstFrom(banding);
  isoln.BackSubstFrom(banding);

  // Because there's plenty of memory, we expect the interleaved solution to
  // use maximum supported columns (same as simple solution)
  ASSERT_EQ(isoln.GetUpperNumColumns(), 8U * sizeof(ResultRow));
  ASSERT_EQ(isoln.GetUpperStartBlock(), 0U);

  // Somewhat oddly, we expect same FP rate as if we had essentially filled
  // up the slots.
  constexpr Index kNumToCheck = 100000;
  KeyGen other_keys_begin("not", 0);
  KeyGen other_keys_end("not", kNumToCheck);

  Index fp_count = 0;
  KeyGen cur = other_keys_begin;
  while (cur != other_keys_end) {
    bool isoln_query_result = isoln.FilterQuery(*cur, hasher);
    bool soln_query_result = soln.FilterQuery(*cur, hasher);
    // Solutions are equivalent
    ASSERT_EQ(isoln_query_result, soln_query_result);
    // And in fact we only expect an FP when ResultRow is 0
    // CHANGE: no longer true because of filling some unused slots
    // with pseudorandom values.
    // ASSERT_EQ(soln_query_result, hasher.GetResultRowFromHash(
    //                                hasher.GetHash(*cur)) == ResultRow{0});
    fp_count += soln_query_result ? 1 : 0;
    ++cur;
  }
  {
    ASSERT_EQ(isoln.ExpectedFpRate(), soln.ExpectedFpRate());
    double expected_fp_count = isoln.ExpectedFpRate() * kNumToCheck;
    EXPECT_LE(fp_count, InfrequentPoissonUpperBound(expected_fp_count));
    EXPECT_GE(fp_count, InfrequentPoissonLowerBound(expected_fp_count));
  }

  // ######################################################
  // Use zero bytes for interleaved solution (key(s) added)

  // Add one key
  KeyGen key_begin("added", 0);
  KeyGen key_end("added", 1);
  ASSERT_TRUE(banding.ResetAndFindSeedToSolve(
      /*slots*/ kCoeffBits, key_begin, key_end, /*first seed*/ 0,
      /* seed mask*/ 0));

  InterleavedSoln isoln2(nullptr, /*bytes*/ 0);

  isoln2.BackSubstFrom(banding);

  ASSERT_EQ(isoln2.GetUpperNumColumns(), 0U);
  ASSERT_EQ(isoln2.GetUpperStartBlock(), 0U);

  // All queries return true
  ASSERT_TRUE(isoln2.FilterQuery(*other_keys_begin, hasher));
  ASSERT_EQ(isoln2.ExpectedFpRate(), 1.0);
}

TEST(RibbonTest, AllowZeroStarts) {
  IMPORT_RIBBON_TYPES_AND_SETTINGS(TypesAndSettings_AllowZeroStarts);
  IMPORT_RIBBON_IMPL_TYPES(TypesAndSettings_AllowZeroStarts);
  using KeyGen = StandardKeyGen;

  InterleavedSoln isoln(nullptr, /*bytes*/ 0);
  SimpleSoln soln;
  Hasher hasher;
  Banding banding;

  KeyGen begin("foo", 0);
  KeyGen end("foo", 1);
  // Can't add 1 entry
  ASSERT_FALSE(banding.ResetAndFindSeedToSolve(/*slots*/ 0, begin, end));

  KeyGen begin_and_end("foo", 123);
  // Can add 0 entries
  ASSERT_TRUE(banding.ResetAndFindSeedToSolve(/*slots*/ 0, begin_and_end,
                                              begin_and_end));

  Seed reseeds = banding.GetOrdinalSeed();
  ASSERT_EQ(reseeds, 0U);
  hasher.SetOrdinalSeed(reseeds);

  // Can construct 0-slot solutions
  isoln.BackSubstFrom(banding);
  soln.BackSubstFrom(banding);

  // Should always return false
  ASSERT_FALSE(isoln.FilterQuery(*begin, hasher));
  ASSERT_FALSE(soln.FilterQuery(*begin, hasher));

  // And report that in FP rate
  ASSERT_EQ(isoln.ExpectedFpRate(), 0.0);
  ASSERT_EQ(soln.ExpectedFpRate(), 0.0);
}

TEST(RibbonTest, RawAndOrdinalSeeds) {
  StandardHasher<TypesAndSettings_Seed64> hasher64;
  StandardHasher<DefaultTypesAndSettings> hasher64_32;
  StandardHasher<TypesAndSettings_Hash32> hasher32;
  StandardHasher<TypesAndSettings_Seed8> hasher8;

  for (uint32_t limit : {0xffU, 0xffffU}) {
    std::vector<bool> seen(limit + 1);
    for (uint32_t i = 0; i < limit; ++i) {
      hasher64.SetOrdinalSeed(i);
      auto raw64 = hasher64.GetRawSeed();
      hasher32.SetOrdinalSeed(i);
      auto raw32 = hasher32.GetRawSeed();
      hasher8.SetOrdinalSeed(static_cast<uint8_t>(i));
      auto raw8 = hasher8.GetRawSeed();
      {
        hasher64_32.SetOrdinalSeed(i);
        auto raw64_32 = hasher64_32.GetRawSeed();
        ASSERT_EQ(raw64_32, raw32);  // Same size seed
      }
      if (i == 0) {
        // Documented that ordinal seed 0 == raw seed 0
        ASSERT_EQ(raw64, 0U);
        ASSERT_EQ(raw32, 0U);
        ASSERT_EQ(raw8, 0U);
      } else {
        // Extremely likely that upper bits are set
        ASSERT_GT(raw64, raw32);
        ASSERT_GT(raw32, raw8);
      }
      // Hashers agree on lower bits
      ASSERT_EQ(static_cast<uint32_t>(raw64), raw32);
      ASSERT_EQ(static_cast<uint8_t>(raw32), raw8);

      // The translation is one-to-one for this size prefix
      uint32_t v = static_cast<uint32_t>(raw32 & limit);
      ASSERT_EQ(raw64 & limit, v);
      ASSERT_FALSE(seen[v]);
      seen[v] = true;
    }
  }
}

namespace {

struct PhsfInputGen {
  PhsfInputGen(const std::string& prefix, uint64_t id) : id_(id) {
    val_.first = prefix;
    ROCKSDB_NAMESPACE::PutFixed64(&val_.first, /*placeholder*/ 0);
  }

  // Prefix (only one required)
  PhsfInputGen& operator++() {
    ++id_;
    return *this;
  }

  const std::pair<std::string, uint8_t>& operator*() {
    // Use multiplication to mix things up a little in the key
    ROCKSDB_NAMESPACE::EncodeFixed64(&val_.first[val_.first.size() - 8],
                                     id_ * uint64_t{0x1500000001});
    // Occasionally repeat values etc.
    val_.second = static_cast<uint8_t>(id_ * 7 / 8);
    return val_;
  }

  const std::pair<std::string, uint8_t>* operator->() { return &**this; }

  bool operator==(const PhsfInputGen& other) {
    // Same prefix is assumed
    return id_ == other.id_;
  }
  bool operator!=(const PhsfInputGen& other) {
    // Same prefix is assumed
    return id_ != other.id_;
  }

  uint64_t id_;
  std::pair<std::string, uint8_t> val_;
};

struct PhsfTypesAndSettings : public DefaultTypesAndSettings {
  static constexpr bool kIsFilter = false;
};
}  // namespace

TEST(RibbonTest, PhsfBasic) {
  IMPORT_RIBBON_TYPES_AND_SETTINGS(PhsfTypesAndSettings);
  IMPORT_RIBBON_IMPL_TYPES(PhsfTypesAndSettings);

  Index num_slots = 12800;
  Index num_to_add = static_cast<Index>(num_slots / 1.02);

  PhsfInputGen begin("in", 0);
  PhsfInputGen end("in", num_to_add);

  std::unique_ptr<char[]> idata(new char[/*bytes*/ num_slots]);
  InterleavedSoln isoln(idata.get(), /*bytes*/ num_slots);
  SimpleSoln soln;
  Hasher hasher;

  {
    Banding banding;
    ASSERT_TRUE(banding.ResetAndFindSeedToSolve(num_slots, begin, end));

    soln.BackSubstFrom(banding);
    isoln.BackSubstFrom(banding);

    hasher.SetOrdinalSeed(banding.GetOrdinalSeed());
  }

  for (PhsfInputGen cur = begin; cur != end; ++cur) {
    ASSERT_EQ(cur->second, soln.PhsfQuery(cur->first, hasher));
    ASSERT_EQ(cur->second, isoln.PhsfQuery(cur->first, hasher));
  }
}

int main(int argc, char** argv) {
  ::testing::InitGoogleTest(&argc, argv);
#ifdef GFLAGS
  ParseCommandLineFlags(&argc, &argv, true);
#endif  // GFLAGS
  return RUN_ALL_TESTS();
}