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https://github.com/ClickHouse/ClickHouse.git
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209 lines
5.0 KiB
C++
209 lines
5.0 KiB
C++
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#pragma once
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#include <unordered_map>
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#include <list>
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#include <memory>
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#include <chrono>
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#include <Poco/ScopedLock.h>
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#include <Poco/Mutex.h>
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#include <DB/Common/Exception.h>
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#include <common/logger_useful.h>
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namespace DB
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{
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template <typename T>
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struct TrivialWeightFunction
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{
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size_t operator()(const T & x) const
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{
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return 1;
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}
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};
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/** Кеш, вытесняющий долго не использовавшиеся и устаревшие записи. thread-safe.
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* WeightFunction - тип, оператор () которого принимает Mapped и возвращает "вес" (примерный размер) этого значения.
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* Кеш начинает выбрасывать значения, когда их суммарный вес превышает max_size и срок годности этих значений истёк.
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* После вставки значения его вес не должен меняться.
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*/
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template <typename TKey, typename TMapped, typename HashFunction = std::hash<TMapped>, typename WeightFunction = TrivialWeightFunction<TMapped> >
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class LRUCache
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{
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public:
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using Key = TKey;
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using Mapped = TMapped;
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using MappedPtr = std::shared_ptr<Mapped>;
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using Delay = std::chrono::seconds;
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private:
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using Clock = std::chrono::steady_clock;
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using Timestamp = Clock::time_point;
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public:
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LRUCache(size_t max_size_, const Delay & expiration_delay_ = Delay::zero())
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: max_size(std::max(1ul, max_size_)), expiration_delay(expiration_delay_) {}
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MappedPtr get(const Key & key)
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{
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Poco::ScopedLock<Poco::FastMutex> lock(mutex);
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auto it = cells.find(key);
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if (it == cells.end())
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{
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++misses;
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return MappedPtr();
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}
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++hits;
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Cell & cell = it->second;
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updateCellTimestamp(cell);
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/// Переместим ключ в конец очереди. Итератор остается валидным.
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queue.splice(queue.end(), queue, cell.queue_iterator);
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return cell.value;
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}
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void set(const Key & key, MappedPtr mapped)
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{
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Poco::ScopedLock<Poco::FastMutex> lock(mutex);
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auto res = cells.emplace(std::piecewise_construct,
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std::forward_as_tuple(key),
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std::forward_as_tuple());
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Cell & cell = res.first->second;
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bool inserted = res.second;
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if (inserted)
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{
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cell.queue_iterator = queue.insert(queue.end(), key);
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}
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else
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{
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current_size -= cell.size;
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queue.splice(queue.end(), queue, cell.queue_iterator);
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}
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cell.value = mapped;
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cell.size = cell.value ? weight_function(*cell.value) : 0;
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current_size += cell.size;
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updateCellTimestamp(cell);
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removeOverflow(cell.timestamp);
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}
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void getStats(size_t & out_hits, size_t & out_misses) const
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{
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Poco::ScopedLock<Poco::FastMutex> lock(mutex);
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out_hits = hits;
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out_misses = misses;
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}
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size_t weight() const
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{
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Poco::ScopedLock<Poco::FastMutex> lock(mutex);
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return current_size;
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}
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size_t count() const
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{
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Poco::ScopedLock<Poco::FastMutex> lock(mutex);
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return cells.size();
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}
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void reset()
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{
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Poco::ScopedLock<Poco::FastMutex> lock(mutex);
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queue.clear();
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cells.clear();
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current_size = 0;
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hits = 0;
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misses = 0;
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current_weight_lost = 0;
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}
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protected:
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size_t current_weight_lost = 0;
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/// Суммарный вес выброшенных из кеша элементов.
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/// Обнуляется каждый раз, когда информация добавляется в Profile events
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private:
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using LRUQueue = std::list<Key>;
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using LRUQueueIterator = typename LRUQueue::iterator;
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struct Cell
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{
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public:
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bool expired(const Timestamp & last_timestamp, const Delay & expiration_delay) const
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{
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return (expiration_delay == Delay::zero()) ||
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((last_timestamp > timestamp) && ((last_timestamp - timestamp) > expiration_delay));
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}
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public:
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MappedPtr value;
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size_t size;
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LRUQueueIterator queue_iterator;
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Timestamp timestamp;
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};
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using Cells = std::unordered_map<Key, Cell, HashFunction>;
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LRUQueue queue;
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Cells cells;
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/// Суммарный вес значений.
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size_t current_size = 0;
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const size_t max_size;
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const Delay expiration_delay;
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mutable Poco::FastMutex mutex;
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size_t hits = 0;
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size_t misses = 0;
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WeightFunction weight_function;
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void updateCellTimestamp(Cell & cell)
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{
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if (expiration_delay != Delay::zero())
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cell.timestamp = Clock::now();
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}
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void removeOverflow(const Timestamp & last_timestamp)
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{
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size_t queue_size = cells.size();
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while ((current_size > max_size) && (queue_size > 1))
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{
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const Key & key = queue.front();
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auto it = cells.find(key);
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if (it == cells.end())
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{
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LOG_ERROR(&Logger::get("LRUCache"), "LRUCache became inconsistent. There must be a bug in it.");
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abort();
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}
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const auto & cell = it->second;
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if (!cell.expired(last_timestamp, expiration_delay))
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break;
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current_size -= cell.size;
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current_weight_lost += cell.size;
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cells.erase(it);
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queue.pop_front();
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--queue_size;
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}
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if (current_size > (1ull << 63))
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{
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LOG_ERROR(&Logger::get("LRUCache"), "LRUCache became inconsistent. There must be a bug in it.");
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abort();
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}
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}
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};
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}
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