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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.
//
// WriteBufferManager is for managing memory allocation for one or more
// MemTables.
#pragma once
#include <atomic>
#include <cstddef>
#include "rocksdb/cache.h"
namespace ROCKSDB_NAMESPACE {
class WriteBufferManager {
public:
// _buffer_size = 0 indicates no limit. Memory won't be capped.
// memory_usage() won't be valid and ShouldFlush() will always return true.
// if `cache` is provided, we'll put dummy entries in the cache and cost
// the memory allocated to the cache. It can be used even if _buffer_size = 0.
explicit WriteBufferManager(size_t _buffer_size,
std::shared_ptr<Cache> cache = {});
// No copying allowed
WriteBufferManager(const WriteBufferManager&) = delete;
WriteBufferManager& operator=(const WriteBufferManager&) = delete;
~WriteBufferManager();
bool enabled() const { return buffer_size_ != 0; }
bool cost_to_cache() const { return cache_rep_ != nullptr; }
// Only valid if enabled()
size_t memory_usage() const {
return memory_used_.load(std::memory_order_relaxed);
}
size_t mutable_memtable_memory_usage() const {
return memory_active_.load(std::memory_order_relaxed);
}
size_t buffer_size() const { return buffer_size_; }
// Should only be called from write thread
bool ShouldFlush() const {
if (enabled()) {
if (mutable_memtable_memory_usage() > mutable_limit_) {
return true;
}
if (memory_usage() >= buffer_size_ &&
mutable_memtable_memory_usage() >= buffer_size_ / 2) {
// If the memory exceeds the buffer size, we trigger more aggressive
// flush. But if already more than half memory is being flushed,
// triggering more flush may not help. We will hold it instead.
return true;
}
}
return false;
}
void ReserveMem(size_t mem) {
if (cache_rep_ != nullptr) {
ReserveMemWithCache(mem);
} else if (enabled()) {
memory_used_.fetch_add(mem, std::memory_order_relaxed);
}
if (enabled()) {
memory_active_.fetch_add(mem, std::memory_order_relaxed);
}
}
// We are in the process of freeing `mem` bytes, so it is not considered
// when checking the soft limit.
void ScheduleFreeMem(size_t mem) {
if (enabled()) {
memory_active_.fetch_sub(mem, std::memory_order_relaxed);
}
}
void FreeMem(size_t mem) {
if (cache_rep_ != nullptr) {
FreeMemWithCache(mem);
} else if (enabled()) {
memory_used_.fetch_sub(mem, std::memory_order_relaxed);
}
}
private:
const size_t buffer_size_;
const size_t mutable_limit_;
std::atomic<size_t> memory_used_;
// Memory that hasn't been scheduled to free.
std::atomic<size_t> memory_active_;
struct CacheRep;
std::unique_ptr<CacheRep> cache_rep_;
void ReserveMemWithCache(size_t mem);
void FreeMemWithCache(size_t mem);
};
} // namespace ROCKSDB_NAMESPACE
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