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Persistent Read Cache (Part 2) Data structure for building persistent read cache index

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Summary:
We expect the persistent read cache to perform at speeds upto 8 GB/s. In order
to accomplish that, we need build a index mechanism which operate in the order
of multiple millions per sec rate.

This patch provide the basic data structure to accomplish that:

(1) Hash table implementation with lock contention spread
    It is based on the StripedHashSet<T> implementation in
    The Art of multiprocessor programming by Maurice Henry & Nir Shavit
(2) LRU implementation
    Place holder algorithm for further optimizing
(3) Evictable Hash Table implementation
    Building block for building index data structure that evicts data like files
    etc

TODO:
(1) Figure if the sharded hash table and LRU can be used instead
(2) Figure if we need to support configurable eviction algorithm for
EvictableHashTable

Test Plan: Run unit tests

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D55785
This commit is contained in:
krad 2016-03-18 15:50:34 -07:00
parent 43afd72bee
commit 1f0142ce19
6 changed files with 1006 additions and 0 deletions
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4
Makefile
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@ -297,6 +297,7 @@ TESTS = \
file_reader_writer_test \ file_reader_writer_test \
block_based_filter_block_test \ block_based_filter_block_test \
full_filter_block_test \ full_filter_block_test \
hash_table_test \
histogram_test \ histogram_test \
inlineskiplist_test \ inlineskiplist_test \
log_test \ log_test \
@ -852,6 +853,9 @@ stringappend_test: utilities/merge_operators/string_append/stringappend_test.o $
redis_test: utilities/redis/redis_lists_test.o $(LIBOBJECTS) $(TESTHARNESS) redis_test: utilities/redis/redis_lists_test.o $(LIBOBJECTS) $(TESTHARNESS)
$(AM_LINK) $(AM_LINK)
hash_table_test: utilities/persistent_cache/hash_table_test.o $(LIBOBJECTS) $(TESTHARNESS)
$(AM_LINK)
histogram_test: util/histogram_test.o $(LIBOBJECTS) $(TESTHARNESS) histogram_test: util/histogram_test.o $(LIBOBJECTS) $(TESTHARNESS)
$(AM_LINK) $(AM_LINK)

226
utilities/persistent_cache/hash_table.h Normal file
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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#pragma once
#include <assert.h>
#include <sys/mman.h>
#include <list>
#include <vector>
#include "include/rocksdb/env.h"
#include "port/port_posix.h"
#include "util/mutexlock.h"
namespace rocksdb {
// HashTable<T, Hash, Equal>
//
// Traditional implementation of hash table with syncronization built on top
// don't perform very well in multi-core scenarios. This is an implementation
// designed for multi-core scenarios with high lock contention.
//
// |<-------- alpha ------------->|
// Buckets Collision list
// ---- +----+ +---+---+--- ...... ---+---+---+
// / | |--->| | | | | |
// / +----+ +---+---+--- ...... ---+---+---+
// / | |
// Locks/ +----+
// +--+/ . .
// | | . .
// +--+ . .
// | | . .
// +--+ . .
// | | . .
// +--+ . .
// \ +----+
// \ | |
// \ +----+
// \ | |
// \---- +----+
//
// The lock contention is spread over an array of locks. This helps improve
// concurrent access. The spine is designed for a certain capacity and load
// factor. When the capacity planning is done correctly we can expect
// O(load_factor = 1) insert, access and remove time.
//
// Micro benchmark on debug build gives about .5 Million/sec rate of insert,
// erase and lookup in parallel (total of about 1.5 Million ops/sec). If the
// blocks were of 4K, the hash table can support a virtual throughput of
// 6 GB/s.
//
// T Object type (contains both key and value)
// Hash Function that returns an hash from type T
// Equal Returns if two objects are equal
// (We need explicit equal for pointer type)
//
template <class T, class Hash, class Equal>
class HashTable {
public:
explicit HashTable(const size_t capacity = 1024 * 1024,
const float load_factor = 2.0, const uint32_t nlocks = 256)
: nbuckets_(load_factor ? capacity / load_factor : 0), nlocks_(nlocks) {
// pre-conditions
assert(capacity);
assert(load_factor);
assert(nbuckets_);
assert(nlocks_);
buckets_.reset(new Bucket[nbuckets_]);
mlock(buckets_.get(), nbuckets_ * sizeof(Bucket));
// initialize locks
locks_.reset(new port::RWMutex[nlocks_]);
mlock(locks_.get(), nlocks_ * sizeof(port::RWMutex));
// post-conditions
assert(buckets_);
assert(locks_);
}
virtual ~HashTable() { AssertEmptyBuckets(); }
//
// Insert given record to hash table
//
bool Insert(const T& t) {
const uint64_t h = Hash()(t);
const uint32_t bucket_idx = h % nbuckets_;
const uint32_t lock_idx = bucket_idx % nlocks_;
WriteLock _(&locks_[lock_idx]);
auto& bucket = buckets_[bucket_idx];
return Insert(&bucket, t);
}
// Lookup hash table
//
// Please note that read lock should be held by the caller. This is because
// the caller owns the data, and should hold the read lock as long as he
// operates on the data.
bool Find(const T& t, T* ret, port::RWMutex** ret_lock) {
const uint64_t h = Hash()(t);
const uint32_t bucket_idx = h % nbuckets_;
const uint32_t lock_idx = bucket_idx % nlocks_;
port::RWMutex& lock = locks_[lock_idx];
lock.ReadLock();
auto& bucket = buckets_[bucket_idx];
if (Find(&bucket, t, ret)) {
*ret_lock = &lock;
return true;
}
lock.ReadUnlock();
return false;
}
//
// Erase a given key from the hash table
//
bool Erase(const T& t, T* ret) {
const uint64_t h = Hash()(t);
const uint32_t bucket_idx = h % nbuckets_;
const uint32_t lock_idx = bucket_idx % nlocks_;
WriteLock _(&locks_[lock_idx]);
auto& bucket = buckets_[bucket_idx];
return Erase(&bucket, t, ret);
}
// Fetch the mutex associated with a key
// This call is used to hold the lock for a given data for extended period of
// time.
port::RWMutex* GetMutex(const T& t) {
const uint64_t h = Hash()(t);
const uint32_t bucket_idx = h % nbuckets_;
const uint32_t lock_idx = bucket_idx % nlocks_;
return &locks_[lock_idx];
}
void Clear(void (*fn)(T)) {
for (uint32_t i = 0; i < nbuckets_; ++i) {
const uint32_t lock_idx = i % nlocks_;
WriteLock _(&locks_[lock_idx]);
for (auto& t : buckets_[i].list_) {
(*fn)(t);
}
buckets_[i].list_.clear();
}
}
protected:
// Models bucket of keys that hash to the same bucket number
struct Bucket {
std::list<T> list_;
};
// Substitute for std::find with custom comparator operator
typename std::list<T>::iterator Find(std::list<T>* list, const T& t) {
for (auto it = list->begin(); it != list->end(); ++it) {
if (Equal()(*it, t)) {
return it;
}
}
return list->end();
}
bool Insert(Bucket* bucket, const T& t) {
// Check if the key already exists
auto it = Find(&bucket->list_, t);
if (it != bucket->list_.end()) {
return false;
}
// insert to bucket
bucket->list_.push_back(t);
return true;
}
bool Find(Bucket* bucket, const T& t, T* ret) {
auto it = Find(&bucket->list_, t);
if (it != bucket->list_.end()) {
if (ret) {
*ret = *it;
}
return true;
}
return false;
}
bool Erase(Bucket* bucket, const T& t, T* ret) {
auto it = Find(&bucket->list_, t);
if (it != bucket->list_.end()) {
if (ret) {
*ret = *it;
}
bucket->list_.erase(it);
return true;
}
return false;
}
// assert that all buckets are empty
void AssertEmptyBuckets() {
#ifndef NDEBUG
for (size_t i = 0; i < nbuckets_; ++i) {
WriteLock _(&locks_[i % nlocks_]);
assert(buckets_[i].list_.empty());
}
#endif
}
const uint32_t nbuckets_; // No. of buckets in the spine
std::unique_ptr<Bucket[]> buckets_; // Spine of the hash buckets
const uint32_t nlocks_; // No. of locks
std::unique_ptr<port::RWMutex[]> locks_; // Granular locks
};
} // namespace rocksdb

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utilities/persistent_cache/hash_table_bench.cc Normal file
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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#include <gflags/gflags.h>
#include <sys/time.h>
#include <unistd.h>
#include <atomic>
#include <functional>
#include <string>
#include <unordered_map>
#include "include/rocksdb/env.h"
#include "port/port_posix.h"
#include "util/mutexlock.h"
#include "utilities/persistent_cache/hash_table.h"
using std::string;
DEFINE_int32(nsec, 10, "nsec");
DEFINE_int32(nthread_write, 1, "insert %");
DEFINE_int32(nthread_read, 1, "lookup %");
DEFINE_int32(nthread_erase, 1, "erase %");
namespace rocksdb {
//
// HashTableImpl interface
//
// Abstraction of a hash table implementation
template <class Key, class Value>
class HashTableImpl {
public:
virtual ~HashTableImpl() {}
virtual bool Insert(const Key& key, const Value& val) = 0;
virtual bool Erase(const Key& key) = 0;
virtual bool Lookup(const Key& key, Value* val) = 0;
};
// HashTableBenchmark
//
// Abstraction to test a given hash table implementation. The test mostly
// focus on insert, lookup and erase. The test can operate in test mode and
// benchmark mode.
class HashTableBenchmark {
public:
explicit HashTableBenchmark(HashTableImpl<size_t, std::string>* impl,
const size_t sec = 10,
const size_t nthread_write = 1,
const size_t nthread_read = 1,
const size_t nthread_erase = 1)
: impl_(impl),
sec_(sec),
ninserts_(0),
nreads_(0),
nerases_(0),
nerases_failed_(0),
quit_(false) {
Prepop();
StartThreads(nthread_write, WriteMain);
StartThreads(nthread_read, ReadMain);
StartThreads(nthread_erase, EraseMain);
uint64_t start = NowInMillSec();
while (!quit_) {
quit_ = NowInMillSec() - start > sec_ * 1000;
/* sleep override */ sleep(1);
}
Env* env = Env::Default();
env->WaitForJoin();
if (sec_) {
printf("Result \n");
printf("====== \n");
printf("insert/sec = %f \n", ninserts_ / static_cast<double>(sec_));
printf("read/sec = %f \n", nreads_ / static_cast<double>(sec_));
printf("erases/sec = %f \n", nerases_ / static_cast<double>(sec_));
const uint64_t ops = ninserts_ + nreads_ + nerases_;
printf("ops/sec = %f \n", ops / static_cast<double>(sec_));
printf("erase fail = %d (%f%%)\n", static_cast<int>(nerases_failed_),
static_cast<float>(nerases_failed_ / nerases_ * 100));
printf("====== \n");
}
}
void RunWrite() {
while (!quit_) {
size_t k = insert_key_++;
std::string tmp(1000, k % 255);
bool status = impl_->Insert(k, tmp);
assert(status);
ninserts_++;
}
}
void RunRead() {
while (!quit_) {
std::string s;
size_t k = random() % max_prepop_key;
bool status = impl_->Lookup(k, &s);
assert(status);
assert(s == std::string(1000, k % 255));
nreads_++;
}
}
void RunErase() {
while (!quit_) {
size_t k = erase_key_++;
bool status = impl_->Erase(k);
nerases_failed_ += !status;
nerases_++;
}
}
private:
// Start threads for a given function
void StartThreads(const size_t n, void (*fn)(void*)) {
Env* env = Env::Default();
for (size_t i = 0; i < n; ++i) {
env->StartThread(fn, this);
}
}
// Prepop the hash table with 1M keys
void Prepop() {
for (size_t i = 0; i < max_prepop_key; ++i) {
bool status = impl_->Insert(i, std::string(1000, i % 255));
assert(status);
}
erase_key_ = insert_key_ = max_prepop_key;
for (size_t i = 0; i < 10 * max_prepop_key; ++i) {
bool status = impl_->Insert(insert_key_++, std::string(1000, 'x'));
assert(status);
}
}
static uint64_t NowInMillSec() {
timeval tv;
gettimeofday(&tv, /*tz=*/nullptr);
return tv.tv_sec * 1000 + tv.tv_usec / 1000;
}
//
// Wrapper functions for thread entry
//
static void WriteMain(void* args) {
reinterpret_cast<HashTableBenchmark*>(args)->RunWrite();
}
static void ReadMain(void* args) {
reinterpret_cast<HashTableBenchmark*>(args)->RunRead();
}
static void EraseMain(void* args) {
reinterpret_cast<HashTableBenchmark*>(args)->RunErase();
}
HashTableImpl<size_t, std::string>* impl_; // Implementation to test
const size_t sec_; // Test time
const size_t max_prepop_key = 1ULL * 1024 * 1024; // Max prepop key
std::atomic<size_t> insert_key_; // Last inserted key
std::atomic<size_t> erase_key_; // Erase key
std::atomic<size_t> ninserts_; // Number of inserts
std::atomic<size_t> nreads_; // Number of reads
std::atomic<size_t> nerases_; // Number of erases
std::atomic<size_t> nerases_failed_; // Number of erases failed
bool quit_; // Should the threads quit ?
};
//
// SimpleImpl
// Lock safe unordered_map implementation
class SimpleImpl : public HashTableImpl<size_t, string> {
public:
bool Insert(const size_t& key, const string& val) override {
WriteLock _(&rwlock_);
map_.insert(make_pair(key, val));
return true;
}
bool Erase(const size_t& key) override {
WriteLock _(&rwlock_);
auto it = map_.find(key);
if (it == map_.end()) {
return false;
}
map_.erase(it);
return true;
}
bool Lookup(const size_t& key, string* val) override {
ReadLock _(&rwlock_);
auto it = map_.find(key);
if (it != map_.end()) {
*val = it->second;
}
return it != map_.end();
}
private:
port::RWMutex rwlock_;
std::unordered_map<size_t, string> map_;
};
//
// GranularLockImpl
// Thread safe custom RocksDB implementation of hash table with granular
// locking
class GranularLockImpl : public HashTableImpl<size_t, string> {
public:
bool Insert(const size_t& key, const string& val) override {
Node n(key, val);
return impl_.Insert(n);
}
bool Erase(const size_t& key) override {
Node n(key, string());
return impl_.Erase(n, nullptr);
}
bool Lookup(const size_t& key, string* val) override {
Node n(key, string());
port::RWMutex* rlock;
bool status = impl_.Find(n, &n, &rlock);
if (status) {
ReadUnlock _(rlock);
*val = n.val_;
}
return status;
}
private:
struct Node {
explicit Node(const size_t key, const string& val) : key_(key), val_(val) {}
size_t key_ = 0;
string val_;
};
struct Hash {
uint64_t operator()(const Node& node) {
return std::hash<uint64_t>()(node.key_);
}
};
struct Equal {
bool operator()(const Node& lhs, const Node& rhs) {
return lhs.key_ == rhs.key_;
}
};
HashTable<Node, Hash, Equal> impl_;
};
} // namespace rocksdb
//
// main
//
int main(int argc, char** argv) {
google::SetUsageMessage(std::string("\nUSAGE:\n") + std::string(argv[0]) +
" [OPTIONS]...");
google::ParseCommandLineFlags(&argc, &argv, false);
//
// Micro benchmark unordered_map
//
printf("Micro benchmarking std::unordered_map \n");
{
rocksdb::SimpleImpl impl;
rocksdb::HashTableBenchmark _(&impl, FLAGS_nsec, FLAGS_nthread_write,
FLAGS_nthread_read, FLAGS_nthread_erase);
}
//
// Micro benchmark scalable hash table
//
printf("Micro benchmarking scalable hash map \n");
{
rocksdb::GranularLockImpl impl;
rocksdb::HashTableBenchmark _(&impl, FLAGS_nsec, FLAGS_nthread_write,
FLAGS_nthread_read, FLAGS_nthread_erase);
}
return 0;
}

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utilities/persistent_cache/hash_table_evictable.h Normal file
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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#pragma once
#include "utilities/persistent_cache/hash_table.h"
#include "utilities/persistent_cache/lrulist.h"
namespace rocksdb {
// Evictable Hash Table
//
// Hash table index where least accessed (or one of the least accessed) elements
// can be evicted.
//
// Please note EvictableHashTable can only be created for pointer type objects
template <class T, class Hash, class Equal>
class EvictableHashTable : private HashTable<T*, Hash, Equal> {
public:
typedef HashTable<T*, Hash, Equal> hash_table;
explicit EvictableHashTable(const size_t capacity = 1024 * 1024,
const float load_factor = 2.0,
const uint32_t nlocks = 256)
: HashTable<T*, Hash, Equal>(capacity, load_factor, nlocks),
lru_lists_(new LRUList<T>[hash_table::nlocks_]) {
assert(lru_lists_);
}
virtual ~EvictableHashTable() { AssertEmptyLRU(); }
//
// Insert given record to hash table (and LRU list)
//
bool Insert(T* t) {
const uint64_t h = Hash()(t);
typename hash_table::Bucket& bucket = GetBucket(h);
LRUListType& lru = GetLRUList(h);
port::RWMutex& lock = GetMutex(h);
WriteLock _(&lock);
if (hash_table::Insert(&bucket, t)) {
lru.Push(t);
return true;
}
return false;
}
//
// Lookup hash table
//
// Please note that read lock should be held by the caller. This is because
// the caller owns the data, and should hold the read lock as long as he
// operates on the data.
bool Find(T* t, T** ret) {
const uint64_t h = Hash()(t);
typename hash_table::Bucket& bucket = GetBucket(h);
LRUListType& lru = GetLRUList(h);
port::RWMutex& lock = GetMutex(h);
ReadLock _(&lock);
if (hash_table::Find(bucket, t, ret)) {
++(*ret)->refs_;
lru.Touch(*ret);
return true;
}
return false;
}
//
// Evict one of the least recently used object
//
T* Evict(const std::function<void(T*)>& fn = nullptr) {
const size_t start_idx = random() % hash_table::nlocks_;
T* t = nullptr;
// iterate from start_idx .. 0 .. start_idx
for (size_t i = 0; !t && i < hash_table::nlocks_; ++i) {
const size_t idx = (start_idx + i) % hash_table::nlocks_;
WriteLock _(&hash_table::locks_[idx]);
LRUListType& lru = lru_lists_[idx];
if (!lru.IsEmpty() && (t = lru.Pop())) {
assert(!t->refs_);
// We got an item to evict, erase from the bucket
const uint64_t h = Hash()(t);
typename hash_table::Bucket& bucket = GetBucket(h);
T* tmp = nullptr;
bool status = hash_table::Erase(&bucket, t, &tmp);
assert(t == tmp);
(void)status;
assert(status);
if (fn) {
fn(t);
}
break;
}
assert(!t);
}
return t;
}
void Clear(void (*fn)(T*)) {
for (uint32_t i = 0; i < hash_table::nbuckets_; ++i) {
const uint32_t lock_idx = i % hash_table::nlocks_;
WriteLock _(&hash_table::locks_[lock_idx]);
auto& lru_list = lru_lists_[lock_idx];
auto& bucket = hash_table::buckets_[i];
for (auto* t : bucket.list_) {
lru_list.Unlink(t);
(*fn)(t);
}
bucket.list_.clear();
}
// make sure that all LRU lists are emptied
AssertEmptyLRU();
}
void AssertEmptyLRU() {
#ifndef NDEBUG
for (uint32_t i = 0; i < hash_table::nlocks_; ++i) {
WriteLock _(&hash_table::locks_[i]);
auto& lru_list = lru_lists_[i];
assert(lru_list.IsEmpty());
}
#endif
}
//
// Fetch the mutex associated with a key
// This call is used to hold the lock for a given data for extended period of
// time.
port::RWMutex* GetMutex(T* t) { return hash_table::GetMutex(t); }
private:
typedef LRUList<T> LRUListType;
typename hash_table::Bucket& GetBucket(const uint64_t h) {
const uint32_t bucket_idx = h % hash_table::nbuckets_;
return hash_table::buckets_[bucket_idx];
}
LRUListType& GetLRUList(const uint64_t h) {
const uint32_t bucket_idx = h % hash_table::nbuckets_;
const uint32_t lock_idx = bucket_idx % hash_table::nlocks_;
return lru_lists_[lock_idx];
}
port::RWMutex& GetMutex(const uint64_t h) {
const uint32_t bucket_idx = h % hash_table::nbuckets_;
const uint32_t lock_idx = bucket_idx % hash_table::nlocks_;
return hash_table::locks_[lock_idx];
}
std::unique_ptr<LRUListType[]> lru_lists_;
};
} // namespace rocksdb

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#include <iostream>
#include <set>
#include <string>
#include "db/db_test_util.h"
#include "util/arena.h"
#include "util/testharness.h"
#include "utilities/persistent_cache/hash_table.h"
#include "utilities/persistent_cache/hash_table_evictable.h"
namespace rocksdb {
struct HashTableTest : public testing::Test {
~HashTableTest() { map_.Clear(&HashTableTest::ClearNode); }
struct Node {
Node() {}
explicit Node(const uint64_t key, const std::string& val = std::string())
: key_(key), val_(val) {}
uint64_t key_ = 0;
std::string val_;
};
struct Equal {
bool operator()(const Node& lhs, const Node& rhs) {
return lhs.key_ == rhs.key_;
}
};
struct Hash {
uint64_t operator()(const Node& node) {
return std::hash<uint64_t>()(node.key_);
}
};
static void ClearNode(Node node) {}
HashTable<Node, Hash, Equal> map_;
};
struct EvictableHashTableTest : public testing::Test {
~EvictableHashTableTest() { map_.Clear(&EvictableHashTableTest::ClearNode); }
struct Node : LRUElement<Node> {
Node() {}
explicit Node(const uint64_t key, const std::string& val = std::string())
: key_(key), val_(val) {}
uint64_t key_ = 0;
std::string val_;
std::atomic<uint32_t> refs_{0};
};
struct Equal {
bool operator()(const Node* lhs, const Node* rhs) {
return lhs->key_ == rhs->key_;
}
};
struct Hash {
uint64_t operator()(const Node* node) {
return std::hash<uint64_t>()(node->key_);
}
};
static void ClearNode(Node* node) {}
EvictableHashTable<Node, Hash, Equal> map_;
};
TEST_F(HashTableTest, TestInsert) {
const uint64_t max_keys = 1024 * 1024;
// insert
for (uint64_t k = 0; k < max_keys; ++k) {
map_.Insert(Node(k, std::string(1000, k % 255)));
}
// verify
for (uint64_t k = 0; k < max_keys; ++k) {
Node val;
port::RWMutex* rlock;
assert(map_.Find(Node(k), &val, &rlock));
rlock->ReadUnlock();
assert(val.val_ == std::string(1000, k % 255));
}
}
TEST_F(HashTableTest, TestErase) {
const uint64_t max_keys = 1024 * 1024;
// insert
for (uint64_t k = 0; k < max_keys; ++k) {
map_.Insert(Node(k, std::string(1000, k % 255)));
}
// erase a few keys randomly
std::set<uint64_t> erased;
for (int i = 0; i < 1024; ++i) {
uint64_t k = random() % max_keys;
if (erased.find(k) != erased.end()) {
continue;
}
assert(map_.Erase(Node(k), /*ret=*/nullptr));
erased.insert(k);
}
// verify
for (uint64_t k = 0; k < max_keys; ++k) {
Node val;
port::RWMutex* rlock = nullptr;
bool status = map_.Find(Node(k), &val, &rlock);
if (erased.find(k) == erased.end()) {
assert(status);
rlock->ReadUnlock();
assert(val.val_ == std::string(1000, k % 255));
} else {
assert(!status);
}
}
}
TEST_F(EvictableHashTableTest, TestEvict) {
const uint64_t max_keys = 1024 * 1024;
// insert
for (uint64_t k = 0; k < max_keys; ++k) {
map_.Insert(new Node(k, std::string(1000, k % 255)));
}
// verify
for (uint64_t k = 0; k < max_keys; ++k) {
Node* val = map_.Evict();
// unfortunately we can't predict eviction value since it is from any one of
// the lock stripe
assert(val);
assert(val->val_ == std::string(1000, val->key_ % 255));
delete val;
}
}
} // namespace rocksdb
int main(int argc, char** argv) {
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}

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utilities/persistent_cache/lrulist.h Normal file
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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#pragma once
#include <atomic>
#include "util/mutexlock.h"
namespace rocksdb {
// LRU element definition
//
// Any object that needs to be part of the LRU algorithm should extend this
// class
template <class T>
struct LRUElement {
explicit LRUElement() : next_(nullptr), prev_(nullptr), refs_(0) {}
virtual ~LRUElement() { assert(!refs_); }
T* next_;
T* prev_;
std::atomic<size_t> refs_;
};
// LRU implementation
//
// In place LRU implementation. There is no copy or allocation involved when
// inserting or removing an element. This makes the data structure slim
template <class T>
class LRUList {
public:
virtual ~LRUList() {
MutexLock _(&lock_);
assert(!head_);
assert(!tail_);
}
// Push element into the LRU at the cold end
inline void Push(T* const t) {
assert(t);
assert(!t->next_);
assert(!t->prev_);
MutexLock _(&lock_);
assert((!head_ && !tail_) || (head_ && tail_));
assert(!head_ || !head_->prev_);
assert(!tail_ || !tail_->next_);
t->next_ = head_;
if (head_) {
head_->prev_ = t;
}
head_ = t;
if (!tail_) {
tail_ = t;
}
}
// Unlink the element from the LRU
inline void Unlink(T* const t) {
MutexLock _(&lock_);
UnlinkImpl(t);
}
// Evict an element from the LRU
inline T* Pop() {
MutexLock _(&lock_);
assert(tail_ && head_);
assert(!tail_->next_);
assert(!head_->prev_);
T* t = head_;
while (t && t->refs_) {
t = t->next_;
}
if (!t) {
// nothing can be evicted
return nullptr;
}
assert(!t->refs_);
// unlike the element
UnlinkImpl(t);
return t;
}
// Move the element from the front of the list to the back of the list
inline void Touch(T* const t) {
MutexLock _(&lock_);
UnlinkImpl(t);
PushBackImpl(t);
}
// Check if the LRU is empty
inline bool IsEmpty() const {
MutexLock _(&lock_);
return !head_ && !tail_;
}
private:
// Unlink an element from the LRU
void UnlinkImpl(T* const t) {
assert(t);
lock_.AssertHeld();
assert(head_ && tail_);
assert(t->prev_ || head_ == t);
assert(t->next_ || tail_ == t);
if (t->prev_) {
t->prev_->next_ = t->next_;
}
if (t->next_) {
t->next_->prev_ = t->prev_;
}
if (tail_ == t) {
tail_ = tail_->prev_;
}
if (head_ == t) {
head_ = head_->next_;
}
t->next_ = t->prev_ = nullptr;
}
// Insert an element at the hot end
inline void PushBack(T* const t) {
MutexLock _(&lock_);
PushBackImpl(t);
}
inline void PushBackImpl(T* const t) {
assert(t);
assert(!t->next_);
assert(!t->prev_);
lock_.AssertHeld();
assert((!head_ && !tail_) || (head_ && tail_));
assert(!head_ || !head_->prev_);
assert(!tail_ || !tail_->next_);
t->prev_ = tail_;
if (tail_) {
tail_->next_ = t;
}
tail_ = t;
if (!head_) {
head_ = tail_;
}
}
mutable port::Mutex lock_; // syncronization primitive
T* head_ = nullptr; // front (cold)
T* tail_ = nullptr; // back (hot)
};
} // namespace rocksdb