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Fix side effect of Remove operation.
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In the original ARC paper, there was no explanation of how Remove should be
handled when the cache is full. The Remove operation would have a side effect
on subsequent Put operations when the cache is not full, which is still
evicting items even though it's clear that there is no need to evict when
the cache is not full.

Now, code has been added to check if the cache is full to avoid performance
degradation.

Also fix c_, it should be max_count.
Also add unittest.

Signed-off-by: Xu Yifeng <[email protected]>
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Xu Yifeng authored and skypexu committed Nov 7, 2023
1 parent c63296b commit 37aba4f
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Showing 2 changed files with 182 additions and 22 deletions.
90 changes: 68 additions & 22 deletions src/common/arc_cache.h
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#include <assert.h>
#include <stdint.h>

#include <algorithm>
#include <list>
#include <memory>
#include <unordered_map>
Expand All @@ -35,9 +36,9 @@ template <typename K, typename V, typename KeyTraits = CacheTraits<K>,
typename ValueTraits = CacheTraits<V>>
class ARCCache : public LRUCacheInterface<K, V> {
public:
ARCCache(int64_t max_count,
ARCCache(uint64_t max_count,
std::shared_ptr<CacheMetrics> cacheMetrics = nullptr)
: c_(max_count/2), p_(0), cacheMetrics_(cacheMetrics) {}
: c_(max_count), p_(0), cacheMetrics_(cacheMetrics) {}

void Put(const K& key, const V& value);
bool Put(const K& key, const V& value, V* eliminated);
Expand All @@ -49,6 +50,8 @@ class ARCCache : public LRUCacheInterface<K, V> {
bool GetLast(const V value, K* key);
bool GetLast(K* key, V* value);
bool GetLast(K* key, V* value, bool (*f)(const V& value));
uint64_t Capacity() const { return c_; }
std::pair<uint64_t, uint64_t> ArcSize() const;

private:
struct BMapVal;
Expand Down Expand Up @@ -158,7 +161,7 @@ class ARCCache : public LRUCacheInterface<K, V> {
map.erase(map_iter);
}

int Count() const { return map.size(); }
uint64_t Count() const { return map.size(); }
};

struct T {
Expand Down Expand Up @@ -238,7 +241,7 @@ class ARCCache : public LRUCacheInterface<K, V> {
map_iter->second.list_iter = --list.end();
}

int Count() const { return map.size(); }
uint64_t Count() const { return map.size(); }

tmap_iter GetLRU() const { return list.begin()->map_iter; }
};
Expand All @@ -262,11 +265,33 @@ class ARCCache : public LRUCacheInterface<K, V> {
return true;
}

bool IsCacheFull() const {
return t1_.Count() + t2_.Count() == c_;
}

void IncreaseP(uint64_t delta) {
if (!IsCacheFull())
return;
if (delta > c_ - p_)
p_ = c_;
else
p_ += delta;
}

void DecreaseP(uint64_t delta) {
if (!IsCacheFull())
return;
if (delta > p_)
p_ = 0;
else
p_ -= delta;
}

bool Replace(const K& k, V* eliminated);

::curve::common::RWLock lock_;
int64_t c_;
int64_t p_;
mutable ::curve::common::RWLock lock_;
uint64_t c_;
uint64_t p_;
B b1_, b2_;
T t1_, t2_;
std::shared_ptr<CacheMetrics> cacheMetrics_;
Expand Down Expand Up @@ -324,12 +349,8 @@ bool ARCCache<K, V, KeyTraits, ValueTraits>::Put(const K& key, const V& value,

bmap_iter b_it;
if (b1_.Find(key, &b_it)) {
if (b1_.Count() >= b2_.Count()) {
p_ += 1;
} else {
p_ += b2_.Count() / b1_.Count();
}
if (p_ > c_) p_ = c_;
uint64_t delta = std::min((uint64_t)1, b2_.Count() / b1_.Count());
IncreaseP(delta);

ret = Replace(key, eliminated);
b1_.Remove(std::move(b_it), cacheMetrics_.get());
Expand All @@ -338,20 +359,16 @@ bool ARCCache<K, V, KeyTraits, ValueTraits>::Put(const K& key, const V& value,
}

if (b2_.Find(key, &b_it)) {
if (b2_.Count() >= b1_.Count()) {
p_ -= 1;
} else {
p_ -= b1_.Count() / b2_.Count();
}
if (p_ < 0) p_ = 0;
uint64_t delta = std::max((uint64_t)1, b1_.Count() / b2_.Count());
DecreaseP(delta);

ret = Replace(key, eliminated);
b2_.Remove(std::move(b_it), cacheMetrics_.get());
t2_.Insert(key, value, cacheMetrics_.get());
return ret;
}

if (t1_.Count() + b1_.Count() == c_) {
if (IsCacheFull() && t1_.Count() + b1_.Count() == c_) {
if (t1_.Count() < c_) {
b1_.RemoveLRU(cacheMetrics_.get());
ret = Replace(key, eliminated);
Expand All @@ -361,7 +378,13 @@ bool ARCCache<K, V, KeyTraits, ValueTraits>::Put(const K& key, const V& value,
} else if (t1_.Count() + b1_.Count() < c_) {
auto total = t1_.Count() + b1_.Count() + t2_.Count() + b2_.Count();
if (total >= c_) {
if (total == 2 * c_) b2_.RemoveLRU(cacheMetrics_.get());
if (total == 2 * c_) {
if (b2_.Count() > 0) {
b2_.RemoveLRU(cacheMetrics_.get());
} else {
b1_.RemoveLRU(cacheMetrics_.get());
}
}
Replace(key, eliminated);
}
}
Expand All @@ -372,11 +395,16 @@ bool ARCCache<K, V, KeyTraits, ValueTraits>::Put(const K& key, const V& value,
template <typename K, typename V, typename KeyTraits, typename ValueTraits>
bool ARCCache<K, V, KeyTraits, ValueTraits>::Replace(const K& k,
V* eliminated) {
if (!IsCacheFull()) {
return false;
}
if (t1_.Count() != 0 &&
((t1_.Count() > p_) || (b2_.Find(k, nullptr) && t1_.Count() == p_))) {
return Move_T_B(&t1_, &b1_, eliminated);
} else {
} else if (t2_.Count() > 0) {
return Move_T_B(&t2_, &b2_, eliminated);
} else {
return Move_T_B(&t1_, &b1_, eliminated);
}
}

Expand All @@ -386,6 +414,16 @@ uint64_t ARCCache<K, V, KeyTraits, ValueTraits>::Size() {
return t1_.Count() + t2_.Count();
}

template <typename K, typename V, typename KeyTraits, typename ValueTraits>
std::pair<uint64_t, uint64_t>
ARCCache<K, V, KeyTraits, ValueTraits>::ArcSize() const {
::curve::common::ReadLockGuard guard(lock_);

return {t1_.Count() + t2_.Count(),
b1_.Count() + b2_.Count()};
}

// This operation detach the key from cache
template <typename K, typename V, typename KeyTraits, typename ValueTraits>
void ARCCache<K, V, KeyTraits, ValueTraits>::Remove(const K& key) {
::curve::common::WriteLockGuard guard(lock_);
Expand All @@ -397,6 +435,14 @@ void ARCCache<K, V, KeyTraits, ValueTraits>::Remove(const K& key) {
return;
}
}
B* bs[]{&b1_, &b2_};
for (auto b : bs) {
bmap_iter it;
if (b->Find(key, &it)) {
b->Remove(std::move(it), cacheMetrics_.get());
return;
}
}
}

template <typename K, typename V, typename KeyTraits, typename ValueTraits>
Expand Down
114 changes: 114 additions & 0 deletions test/common/arc_cache_test.cpp
Original file line number Diff line number Diff line change
@@ -0,0 +1,114 @@
/*
* Copyright (c) 2020 NetEase Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

/*
* Project: curve
* Created Date: 20211010
* Author: xuchaojie,lixiaocui
*/

#include <gtest/gtest.h>
#include <glog/logging.h>
#include <cstdint>

#include "src/common/lru_cache.h"

namespace curve {
namespace common {

TEST(ArcTest, test_cache_create) {
int maxCount = 5;
auto cache = std::make_shared<ARCCache<int, int>>(maxCount,
std::make_shared<CacheMetrics>("Cache"));

ASSERT_EQ(cache->Capacity() == 5);
ASSERT_EQ(cache->Size() == 0);
}

TEST(ArcTest, test_cache_put) {
int maxCount = 5;
auto cache = std::make_shared<ARCCache<int, int>>(maxCount,
std::make_shared<CacheMetrics>("Cache"));

for (int i = 0; i < maxCount; ++i) {
cache->Put(i, i);
}

ASSERT_TRUE(cache->Size() == maxCount);

int v;
for (int i = 0; i < maxCount; ++i) {
ASSERT_TRUE(cache->Get(i, &v));
ASSERT_EQ(v, i);
}
}

TEST(ArcTest, test_cache_retire) {
int maxCount = 5;
auto cache = std::make_shared<ARCCache<int, int>>(maxCount,
std::make_shared<CacheMetrics>("Cache"));

for (int i = 0; i < maxCount+1; ++i) {
cache->Put(i, i);
}

ASSERT_TRUE(cache->Size() == maxCount);

int v;
ASSERT_TRUE(cache->Get(0, &v) == false);
for (int i = 1; i < maxCount+1; ++i) {
ASSERT_TRUE(cache->Get(i, &v));
ASSERT_EQ(v, i);
}

for (int i = 100; i < 200; ++i) {
cache->Put(i, i);
}

auto s = cache->ArcSize();
ASSERT_TRUE(s.first + s.second <= 2 * maxCount);
}

TEST(ArcTest, test_cache_remove) {
int maxCount = 5;
auto cache = std::make_shared<ARCCache<int, int>>(maxCount,
std::make_shared<CacheMetrics>("Cache"));

for (int i = 0; i < maxCount; ++i) {
cache->Put(i, i);
}

cache->Remove(0);
int v;
ASSERT_FALSE(cache->Get(0, &v));
ASSERT_TRUE(cache->Size() == maxCount-1);

for (int i = 1; i < maxCount; ++i) {
ASSERT_TRUE(cache->Get(i, &v));
ASSERT_EQ(v, i);
}

for (int i = 100; i < 200; ++i) {
cache->Put(i, i);
}

auto s = cache->ArcSize();
ASSERT_TRUE(s.first + s.second <= 2 * maxCount);
}

} // namespace common
} // namespace curve

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