mirror of https://github.com/facebook/rocksdb.git
98 lines
4.1 KiB
C++
98 lines
4.1 KiB
C++
// Copyright (c) 2011-present, 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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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include <atomic>
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#include <cstddef>
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#include <cstdint>
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#include <memory>
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#include <vector>
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#include "cache/cache_entry_roles.h"
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#include "rocksdb/cache.h"
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#include "rocksdb/slice.h"
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#include "rocksdb/status.h"
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#include "table/block_based/block_based_table_reader.h"
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#include "util/coding.h"
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namespace ROCKSDB_NAMESPACE {
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// CacheReservationManager is for reserving cache space for the memory used
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// through inserting/releasing dummy entries in the cache.
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// This class is not thread-safe.
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class CacheReservationManager {
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public:
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// Construct a CacheReservationManager
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// @param cache The cache where dummy entries are inserted and released for
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// reserving cache space
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// @param delayed_decrease If set true, then dummy entries won't be released
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// immediately when memory usage decreases.
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// Instead, it will be released when the memory usage
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// decreases to 3/4 of what we have reserved so far.
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// This is for saving some future dummy entry
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// insertion when memory usage increases are likely to
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// happen in the near future.
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explicit CacheReservationManager(std::shared_ptr<Cache> cache,
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bool delayed_decrease = false);
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// no copy constructor, copy assignment, move constructor, move assignment
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CacheReservationManager(const CacheReservationManager &) = delete;
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CacheReservationManager &operator=(const CacheReservationManager &) = delete;
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CacheReservationManager(CacheReservationManager &&) = delete;
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CacheReservationManager &operator=(CacheReservationManager &&) = delete;
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~CacheReservationManager();
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template <CacheEntryRole R>
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// Insert and release dummy entries in the cache to
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// match the size of total dummy entries with the smallest multiple of
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// kSizeDummyEntry that is greater than or equal to new_mem_used
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//
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// Insert dummy entries if new_memory_used > cache_allocated_size_;
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//
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// Release dummy entries if new_memory_used < cache_allocated_size_
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// (and new_memory_used < cache_allocated_size_ * 3/4
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// when delayed_decrease is set true);
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//
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// Keey dummy entries the same if (1) new_memory_used == cache_allocated_size_
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// or (2) new_memory_used is in the interval of
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// [cache_allocated_size_ * 3/4, cache_allocated_size) when delayed_decrease
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// is set true.
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//
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// @param new_memory_used The number of bytes used by new memory
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// @return On inserting dummy entries, it returns Status::OK() if all dummy
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// entry insertions succeed. Otherwise, it returns the first non-ok status;
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// On releasing dummy entries, it always returns Status::OK().
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// On keeping dummy entries the same, it always returns Status::OK().
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Status UpdateCacheReservation(std::size_t new_memory_used);
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std::size_t GetTotalReservedCacheSize();
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private:
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static constexpr std::size_t kSizeDummyEntry = 256 * 1024;
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// The key will be longer than keys for blocks in SST files so they won't
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// conflict.
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static const std::size_t kCacheKeyPrefixSize =
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BlockBasedTable::kMaxCacheKeyPrefixSize + kMaxVarint64Length;
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Slice GetNextCacheKey();
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template <CacheEntryRole R>
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Status IncreaseCacheReservation(std::size_t new_mem_used);
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Status DecreaseCacheReservation(std::size_t new_mem_used);
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std::shared_ptr<Cache> cache_;
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bool delayed_decrease_;
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std::atomic<std::size_t> cache_allocated_size_;
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std::vector<Cache::Handle *> dummy_handles_;
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std::uint64_t next_cache_key_id_ = 0;
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// The non-prefix part will be updated according to the ID to use.
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char cache_key_[kCacheKeyPrefixSize + kMaxVarint64Length];
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};
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} // namespace ROCKSDB_NAMESPACE
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