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Improve accuracy testing for DynamicBloom (#5805)

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Summary:
DynamicBloom unit test now tests non-sequential as well as
sequential keys in testing FP rates. Also now verifies larger structures.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5805

Test Plan: thisisthetest

Differential Revision: D17398109

Pulled By: pdillinger

fbshipit-source-id: 374074206c76d242efa378afc27830448a0e892a
This commit is contained in:
Peter Dillinger 2019-09-16 09:35:51 -07:00 committed by Facebook Github Bot
parent 0b59ef519f
commit 915d72d849
1 changed files with 49 additions and 23 deletions
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72
util/dynamic_bloom_test.cc
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@ -36,10 +36,25 @@ DEFINE_bool(enable_perf, false, "");
namespace rocksdb {
static Slice Key(uint64_t i, char* buffer) {
memcpy(buffer, &i, sizeof(i));
return Slice(buffer, sizeof(i));
}
struct KeyMaker {
uint64_t a;
uint64_t b;
// Sequential, within a hash function block
inline Slice Seq(uint64_t i) {
a = i;
return Slice(reinterpret_cast<char *>(&a), sizeof(a));
}
// Not quite sequential, varies across hash function blocks
inline Slice Nonseq(uint64_t i) {
a = i;
b = i * 123;
return Slice(reinterpret_cast<char *>(this), sizeof(*this));
}
inline Slice Key(uint64_t i, bool nonseq) {
return nonseq ? Nonseq(i) : Seq(i);
}
};
class DynamicBloomTest : public testing::Test {};
@ -100,13 +115,13 @@ static uint32_t NextNum(uint32_t num) {
} else if (num < 1000) {
num += 100;
} else {
num += 1000;
num = num * 26 / 10;
}
return num;
}
TEST_F(DynamicBloomTest, VaryingLengths) {
char buffer[sizeof(uint64_t)];
KeyMaker km;
// Count number of filters that significantly exceed the false positive rate
int mediocre_filters = 0;
@ -116,47 +131,53 @@ TEST_F(DynamicBloomTest, VaryingLengths) {
fprintf(stderr, "bits_per_key: %d num_probes: %d\n", FLAGS_bits_per_key,
num_probes);
for (uint32_t num = 1; num <= 10000; num = NextNum(num)) {
// NB: FP rate impact of 32-bit hash is noticeable starting around 10M keys.
// But that effect is hidden if using sequential keys (unique hashes).
for (bool nonseq : {false, true}) {
const uint32_t max_num = FLAGS_enable_perf ? 40000000 : 400000;
for (uint32_t num = 1; num <= max_num; num = NextNum(num)) {
uint32_t bloom_bits = 0;
Arena arena;
bloom_bits = num * FLAGS_bits_per_key;
DynamicBloom bloom(&arena, bloom_bits, num_probes);
for (uint64_t i = 0; i < num; i++) {
bloom.Add(Key(i, buffer));
ASSERT_TRUE(bloom.MayContain(Key(i, buffer)));
bloom.Add(km.Key(i, nonseq));
ASSERT_TRUE(bloom.MayContain(km.Key(i, nonseq)));
}
// All added keys must match
for (uint64_t i = 0; i < num; i++) {
ASSERT_TRUE(bloom.MayContain(Key(i, buffer))) << "Num " << num
<< "; key " << i;
ASSERT_TRUE(bloom.MayContain(km.Key(i, nonseq)));
}
// Check false positive rate
int result = 0;
for (uint64_t i = 0; i < 10000; i++) {
if (bloom.MayContain(Key(i + 1000000000, buffer))) {
for (uint64_t i = 0; i < 30000; i++) {
if (bloom.MayContain(km.Key(i + 1000000000, nonseq))) {
result++;
}
}
double rate = result / 10000.0;
double rate = result / 30000.0;
fprintf(stderr,
"False positives: %5.2f%% @ num = %6u, bloom_bits = %6u\n",
rate * 100.0, num, bloom_bits);
"False positives (%s keys): "
"%5.2f%% @ num = %6u, bloom_bits = %6u\n",
nonseq ? "nonseq" : "seq", rate * 100.0, num, bloom_bits);
if (rate > 0.0125)
mediocre_filters++; // Allowed, but not too often
else
good_filters++;
}
}
fprintf(stderr, "Filters: %d good, %d mediocre\n", good_filters,
mediocre_filters);
ASSERT_LE(mediocre_filters, good_filters / 5);
ASSERT_LE(mediocre_filters, good_filters / 25);
}
TEST_F(DynamicBloomTest, perf) {
KeyMaker km;
StopWatchNano timer(Env::Default());
uint32_t num_probes = static_cast<uint32_t>(FLAGS_num_probes);
@ -173,7 +194,7 @@ TEST_F(DynamicBloomTest, perf) {
timer.Start();
for (uint64_t i = 1; i <= num_keys; ++i) {
std_bloom.Add(Slice(reinterpret_cast<const char*>(&i), 8));
std_bloom.Add(km.Seq(i));
}
uint64_t elapsed = timer.ElapsedNanos();
@ -183,7 +204,7 @@ TEST_F(DynamicBloomTest, perf) {
uint32_t count = 0;
timer.Start();
for (uint64_t i = 1; i <= num_keys; ++i) {
if (std_bloom.MayContain(Slice(reinterpret_cast<const char*>(&i), 8))) {
if (std_bloom.MayContain(km.Seq(i))) {
++count;
}
}
@ -203,6 +224,9 @@ TEST_F(DynamicBloomTest, concurrent_with_perf) {
uint32_t num_threads = 4;
std::vector<port::Thread> threads;
// NB: Uses sequential keys for speed, but that hides the FP rate
// impact of 32-bit hash, which is noticeable starting around 10M keys
// when they vary across hashing blocks.
for (uint32_t m = 1; m <= m_limit; ++m) {
Arena arena;
const uint32_t num_keys = m * 8 * 1024 * 1024;
@ -213,11 +237,11 @@ TEST_F(DynamicBloomTest, concurrent_with_perf) {
std::atomic<uint64_t> elapsed(0);
std::function<void(size_t)> adder([&](size_t t) {
KeyMaker km;
StopWatchNano timer(Env::Default());
timer.Start();
for (uint64_t i = 1 + t; i <= num_keys; i += num_threads) {
std_bloom.AddConcurrently(
Slice(reinterpret_cast<const char*>(&i), 8));
std_bloom.AddConcurrently(km.Seq(i));
}
elapsed += timer.ElapsedNanos();
});
@ -235,11 +259,12 @@ TEST_F(DynamicBloomTest, concurrent_with_perf) {
elapsed = 0;
std::function<void(size_t)> hitter([&](size_t t) {
KeyMaker km;
StopWatchNano timer(Env::Default());
timer.Start();
for (uint64_t i = 1 + t; i <= num_keys; i += num_threads) {
bool f =
std_bloom.MayContain(Slice(reinterpret_cast<const char*>(&i), 8));
std_bloom.MayContain(km.Seq(i));
ASSERT_TRUE(f);
}
elapsed += timer.ElapsedNanos();
@ -259,12 +284,13 @@ TEST_F(DynamicBloomTest, concurrent_with_perf) {
elapsed = 0;
std::atomic<uint32_t> false_positives(0);
std::function<void(size_t)> misser([&](size_t t) {
KeyMaker km;
StopWatchNano timer(Env::Default());
timer.Start();
for (uint64_t i = num_keys + 1 + t; i <= 2 * num_keys;
i += num_threads) {
bool f =
std_bloom.MayContain(Slice(reinterpret_cast<const char*>(&i), 8));
std_bloom.MayContain(km.Seq(i));
if (f) {
++false_positives;
}