ebab2e2d42
Summary: Closes https://github.com/facebook/rocksdb/pull/3018 Differential Revision: D6079011 Pulled By: yiwu-arbug fbshipit-source-id: 988a721e7e7617967859dba71d660fc69f4dff57
169 lines
4.7 KiB
C++
169 lines
4.7 KiB
C++
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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#pragma once
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#ifndef ROCKSDB_LITE
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#include <functional>
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#include "util/random.h"
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#include "utilities/persistent_cache/hash_table.h"
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#include "utilities/persistent_cache/lrulist.h"
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namespace rocksdb {
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// Evictable Hash Table
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//
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// Hash table index where least accessed (or one of the least accessed) elements
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// can be evicted.
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//
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// Please note EvictableHashTable can only be created for pointer type objects
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template <class T, class Hash, class Equal>
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class EvictableHashTable : private HashTable<T*, Hash, Equal> {
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public:
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typedef HashTable<T*, Hash, Equal> hash_table;
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explicit EvictableHashTable(const size_t capacity = 1024 * 1024,
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const float load_factor = 2.0,
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const uint32_t nlocks = 256)
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: HashTable<T*, Hash, Equal>(capacity, load_factor, nlocks),
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lru_lists_(new LRUList<T>[hash_table::nlocks_]) {
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assert(lru_lists_);
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}
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virtual ~EvictableHashTable() { AssertEmptyLRU(); }
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//
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// Insert given record to hash table (and LRU list)
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//
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bool Insert(T* t) {
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const uint64_t h = Hash()(t);
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typename hash_table::Bucket& bucket = GetBucket(h);
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LRUListType& lru = GetLRUList(h);
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port::RWMutex& lock = GetMutex(h);
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WriteLock _(&lock);
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if (hash_table::Insert(&bucket, t)) {
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lru.Push(t);
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return true;
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}
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return false;
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}
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//
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// Lookup hash table
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//
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// Please note that read lock should be held by the caller. This is because
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// the caller owns the data, and should hold the read lock as long as he
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// operates on the data.
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bool Find(T* t, T** ret) {
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const uint64_t h = Hash()(t);
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typename hash_table::Bucket& bucket = GetBucket(h);
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LRUListType& lru = GetLRUList(h);
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port::RWMutex& lock = GetMutex(h);
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ReadLock _(&lock);
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if (hash_table::Find(&bucket, t, ret)) {
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++(*ret)->refs_;
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lru.Touch(*ret);
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return true;
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}
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return false;
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}
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//
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// Evict one of the least recently used object
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//
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T* Evict(const std::function<void(T*)>& fn = nullptr) {
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uint32_t random = Random::GetTLSInstance()->Next();
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const size_t start_idx = random % hash_table::nlocks_;
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T* t = nullptr;
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// iterate from start_idx .. 0 .. start_idx
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for (size_t i = 0; !t && i < hash_table::nlocks_; ++i) {
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const size_t idx = (start_idx + i) % hash_table::nlocks_;
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WriteLock _(&hash_table::locks_[idx]);
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LRUListType& lru = lru_lists_[idx];
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if (!lru.IsEmpty() && (t = lru.Pop()) != nullptr) {
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assert(!t->refs_);
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// We got an item to evict, erase from the bucket
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const uint64_t h = Hash()(t);
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typename hash_table::Bucket& bucket = GetBucket(h);
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T* tmp = nullptr;
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bool status = hash_table::Erase(&bucket, t, &tmp);
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assert(t == tmp);
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(void)status;
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assert(status);
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if (fn) {
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fn(t);
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}
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break;
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}
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assert(!t);
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}
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return t;
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}
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void Clear(void (*fn)(T*)) {
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for (uint32_t i = 0; i < hash_table::nbuckets_; ++i) {
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const uint32_t lock_idx = i % hash_table::nlocks_;
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WriteLock _(&hash_table::locks_[lock_idx]);
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auto& lru_list = lru_lists_[lock_idx];
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auto& bucket = hash_table::buckets_[i];
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for (auto* t : bucket.list_) {
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lru_list.Unlink(t);
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(*fn)(t);
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}
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bucket.list_.clear();
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}
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// make sure that all LRU lists are emptied
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AssertEmptyLRU();
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}
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void AssertEmptyLRU() {
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#ifndef NDEBUG
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for (uint32_t i = 0; i < hash_table::nlocks_; ++i) {
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WriteLock _(&hash_table::locks_[i]);
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auto& lru_list = lru_lists_[i];
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assert(lru_list.IsEmpty());
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}
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#endif
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}
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//
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// Fetch the mutex associated with a key
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// This call is used to hold the lock for a given data for extended period of
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// time.
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port::RWMutex* GetMutex(T* t) { return hash_table::GetMutex(t); }
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private:
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typedef LRUList<T> LRUListType;
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typename hash_table::Bucket& GetBucket(const uint64_t h) {
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const uint32_t bucket_idx = h % hash_table::nbuckets_;
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return hash_table::buckets_[bucket_idx];
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}
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LRUListType& GetLRUList(const uint64_t h) {
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const uint32_t bucket_idx = h % hash_table::nbuckets_;
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const uint32_t lock_idx = bucket_idx % hash_table::nlocks_;
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return lru_lists_[lock_idx];
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}
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port::RWMutex& GetMutex(const uint64_t h) {
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const uint32_t bucket_idx = h % hash_table::nbuckets_;
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const uint32_t lock_idx = bucket_idx % hash_table::nlocks_;
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return hash_table::locks_[lock_idx];
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}
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std::unique_ptr<LRUListType[]> lru_lists_;
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};
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} // namespace rocksdb
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#endif
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