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rocksdb/cache/cache_reservation_manager.h

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include <atomic>
#include <cstddef>
#include <cstdint>
#include <memory>
#include <mutex>
#include <vector>
#include "cache/cache_entry_roles.h"
#include "cache/cache_key.h"
#include "rocksdb/cache.h"
#include "rocksdb/slice.h"
#include "rocksdb/status.h"
#include "util/coding.h"
namespace ROCKSDB_NAMESPACE {
// CacheReservationManager is an interface for reserving cache space for the
// memory used
class CacheReservationManager {
public:
// CacheReservationHandle is for managing the lifetime of a cache reservation
// for an incremental amount of memory used (i.e, incremental_memory_used)
class CacheReservationHandle {
public:
virtual ~CacheReservationHandle() {}
};
virtual ~CacheReservationManager() {}
virtual Status UpdateCacheReservation(std::size_t new_memory_used) = 0;
virtual Status MakeCacheReservation(
std::size_t incremental_memory_used,
std::unique_ptr<CacheReservationManager::CacheReservationHandle>
*handle) = 0;
virtual std::size_t GetTotalReservedCacheSize() = 0;
virtual std::size_t GetTotalMemoryUsed() = 0;
};
// CacheReservationManagerImpl implements interface CacheReservationManager
// for reserving cache space for the memory used by inserting/releasing dummy
// entries in the cache.
//
// This class is NOT thread-safe, except that GetTotalReservedCacheSize()
// can be called without external synchronization.
template <CacheEntryRole R>
class CacheReservationManagerImpl
: public CacheReservationManager,
public std::enable_shared_from_this<CacheReservationManagerImpl<R>> {
public:
class CacheReservationHandle
: public CacheReservationManager::CacheReservationHandle {
public:
CacheReservationHandle(
std::size_t incremental_memory_used,
std::shared_ptr<CacheReservationManagerImpl> cache_res_mgr);
~CacheReservationHandle() override;
private:
std::size_t incremental_memory_used_;
std::shared_ptr<CacheReservationManagerImpl> cache_res_mgr_;
};
// Construct a CacheReservationManagerImpl
// @param cache The cache where dummy entries are inserted and released for
// reserving cache space
// @param delayed_decrease If set true, then dummy entries won't be released
// immediately when memory usage decreases.
// Instead, it will be released when the memory usage
// decreases to 3/4 of what we have reserved so far.
// This is for saving some future dummy entry
// insertion when memory usage increases are likely to
// happen in the near future.
//
// REQUIRED: cache is not nullptr
explicit CacheReservationManagerImpl(std::shared_ptr<Cache> cache,
bool delayed_decrease = false);
// no copy constructor, copy assignment, move constructor, move assignment
CacheReservationManagerImpl(const CacheReservationManagerImpl &) = delete;
CacheReservationManagerImpl &operator=(const CacheReservationManagerImpl &) =
delete;
CacheReservationManagerImpl(CacheReservationManagerImpl &&) = delete;
CacheReservationManagerImpl &operator=(CacheReservationManagerImpl &&) =
delete;
~CacheReservationManagerImpl() override;
// One of the two ways of reserving/releasing cache space,
// see MakeCacheReservation() for the other.
//
// Use ONLY one of these two ways to prevent unexpected behavior.
//
// Insert and release dummy entries in the cache to
// match the size of total dummy entries with the least multiple of
// kSizeDummyEntry greater than or equal to new_mem_used
//
// Insert dummy entries if new_memory_used > cache_allocated_size_;
//
// Release dummy entries if new_memory_used < cache_allocated_size_
// (and new_memory_used < cache_allocated_size_ * 3/4
// when delayed_decrease is set true);
//
// Keey dummy entries the same if (1) new_memory_used == cache_allocated_size_
// or (2) new_memory_used is in the interval of
// [cache_allocated_size_ * 3/4, cache_allocated_size) when delayed_decrease
// is set true.
//
// @param new_memory_used The number of bytes used by new memory
// The most recent new_memoy_used passed in will be returned
// in GetTotalMemoryUsed() even when the call return non-ok status.
//
// Since the class is NOT thread-safe, external synchronization on the
// order of calling UpdateCacheReservation() is needed if you want
// GetTotalMemoryUsed() indeed returns the latest memory used.
//
// @return On inserting dummy entries, it returns Status::OK() if all dummy
// entry insertions succeed.
// Otherwise, it returns the first non-ok status;
// On releasing dummy entries, it always returns Status::OK().
// On keeping dummy entries the same, it always returns Status::OK().
Status UpdateCacheReservation(std::size_t new_memory_used) override;
// One of the two ways of reserving cache space and releasing is done through
// destruction of CacheReservationHandle.
// See UpdateCacheReservation() for the other way.
//
// Use ONLY one of these two ways to prevent unexpected behavior.
//
// Insert dummy entries in the cache for the incremental memory usage
// to match the size of total dummy entries with the least multiple of
// kSizeDummyEntry greater than or equal to the total memory used.
//
// A CacheReservationHandle is returned as an output parameter.
// The reserved dummy entries are automatically released on the destruction of
// this handle, which achieves better RAII per cache reservation.
//
// WARNING: Deallocate all the handles of the CacheReservationManager object
// before deallocating the object to prevent unexpected behavior.
//
// @param incremental_memory_used The number of bytes increased in memory
// usage.
//
// Calling GetTotalMemoryUsed() afterward will return the total memory
// increased by this number, even when calling MakeCacheReservation()
// returns non-ok status.
//
// Since the class is NOT thread-safe, external synchronization in
// calling MakeCacheReservation() is needed if you want
// GetTotalMemoryUsed() indeed returns the latest memory used.
//
// @param handle An pointer to std::unique_ptr<CacheReservationHandle> that
// manages the lifetime of the cache reservation represented by the
// handle.
//
// @return It returns Status::OK() if all dummy
// entry insertions succeed.
// Otherwise, it returns the first non-ok status;
//
// REQUIRES: handle != nullptr
Status MakeCacheReservation(
std::size_t incremental_memory_used,
std::unique_ptr<CacheReservationManager::CacheReservationHandle> *handle)
override;
// Return the size of the cache (which is a multiple of kSizeDummyEntry)
// successfully reserved by calling UpdateCacheReservation().
//
// When UpdateCacheReservation() returns non-ok status,
// calling GetTotalReservedCacheSize() after that might return a slightly
// smaller number than the actual reserved cache size due to
// the returned number will always be a multiple of kSizeDummyEntry
// and cache full might happen in the middle of inserting a dummy entry.
std::size_t GetTotalReservedCacheSize() override;
// Return the latest total memory used indicated by the most recent call of
// UpdateCacheReservation(std::size_t new_memory_used);
std::size_t GetTotalMemoryUsed() override;
static constexpr std::size_t GetDummyEntrySize() { return kSizeDummyEntry; }
// For testing only - it is to help ensure the NoopDeleterForRole<R>
// accessed from CacheReservationManagerImpl and the one accessed from the
// test are from the same translation units
static Cache::DeleterFn TEST_GetNoopDeleterForRole();
private:
static constexpr std::size_t kSizeDummyEntry = 256 * 1024;
Slice GetNextCacheKey();
Status ReleaseCacheReservation(std::size_t incremental_memory_used);
Status IncreaseCacheReservation(std::size_t new_mem_used);
Status DecreaseCacheReservation(std::size_t new_mem_used);
std::shared_ptr<Cache> cache_;
bool delayed_decrease_;
std::atomic<std::size_t> cache_allocated_size_;
std::size_t memory_used_;
std::vector<Cache::Handle *> dummy_handles_;
CacheKey cache_key_;
};
class ConcurrentCacheReservationManager
: public CacheReservationManager,
public std::enable_shared_from_this<ConcurrentCacheReservationManager> {
public:
class CacheReservationHandle
: public CacheReservationManager::CacheReservationHandle {
public:
CacheReservationHandle(
std::shared_ptr<ConcurrentCacheReservationManager> cache_res_mgr,
std::unique_ptr<CacheReservationManager::CacheReservationHandle>
cache_res_handle) {
assert(cache_res_mgr && cache_res_handle);
cache_res_mgr_ = cache_res_mgr;
cache_res_handle_ = std::move(cache_res_handle);
}
~CacheReservationHandle() override {
std::lock_guard<std::mutex> lock(cache_res_mgr_->cache_res_mgr_mu_);
cache_res_handle_.reset();
}
private:
std::shared_ptr<ConcurrentCacheReservationManager> cache_res_mgr_;
std::unique_ptr<CacheReservationManager::CacheReservationHandle>
cache_res_handle_;
};
explicit ConcurrentCacheReservationManager(
std::shared_ptr<CacheReservationManager> cache_res_mgr) {
cache_res_mgr_ = std::move(cache_res_mgr);
}
ConcurrentCacheReservationManager(const ConcurrentCacheReservationManager &) =
delete;
ConcurrentCacheReservationManager &operator=(
const ConcurrentCacheReservationManager &) = delete;
ConcurrentCacheReservationManager(ConcurrentCacheReservationManager &&) =
delete;
ConcurrentCacheReservationManager &operator=(
ConcurrentCacheReservationManager &&) = delete;
~ConcurrentCacheReservationManager() override {}
inline Status UpdateCacheReservation(std::size_t new_memory_used) override {
std::lock_guard<std::mutex> lock(cache_res_mgr_mu_);
return cache_res_mgr_->UpdateCacheReservation(new_memory_used);
}
inline Status MakeCacheReservation(
std::size_t incremental_memory_used,
std::unique_ptr<CacheReservationManager::CacheReservationHandle> *handle)
override {
std::unique_ptr<CacheReservationManager::CacheReservationHandle>
wrapped_handle;
Status s;
{
std::lock_guard<std::mutex> lock(cache_res_mgr_mu_);
s = cache_res_mgr_->MakeCacheReservation(incremental_memory_used,
&wrapped_handle);
}
(*handle).reset(
new ConcurrentCacheReservationManager::CacheReservationHandle(
std::enable_shared_from_this<
ConcurrentCacheReservationManager>::shared_from_this(),
std::move(wrapped_handle)));
return s;
}
inline std::size_t GetTotalReservedCacheSize() override {
return cache_res_mgr_->GetTotalReservedCacheSize();
}
inline std::size_t GetTotalMemoryUsed() override {
std::lock_guard<std::mutex> lock(cache_res_mgr_mu_);
return cache_res_mgr_->GetTotalMemoryUsed();
}
private:
std::mutex cache_res_mgr_mu_;
std::shared_ptr<CacheReservationManager> cache_res_mgr_;
};
} // namespace ROCKSDB_NAMESPACE