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rocksdb/cache/cache_reservation_manager.cc

131 lines
5.1 KiB

Refactor WriteBufferManager::CacheRep into CacheReservationManager (#8506) Summary: Context: To help cap various memory usage by a single limit of the block cache capacity, we charge the memory usage through inserting/releasing dummy entries in the block cache. CacheReservationManager is such a class (non thread-safe) responsible for inserting/removing dummy entries to reserve cache space for memory used by the class user. - Refactored the inner private class CacheRep of WriteBufferManager into public CacheReservationManager class for reusability such as for https://github.com/facebook/rocksdb/pull/8428 - Encapsulated implementation details of cache key generation and dummy entries insertion/release in cache reservation as discussed in https://github.com/facebook/rocksdb/pull/8506#discussion_r666550838 - Consolidated increase/decrease cache reservation into one API - UpdateCacheReservation. - Adjusted the previous dummy entry release algorithm in decreasing cache reservation to be loop-releasing dummy entries to stay symmetric to dummy entry insertion algorithm - Made the previous dummy entry release algorithm in delayed decrease mode more aggressive for better decreasing cache reservation when memory used is less likely to increase back. Previously, the algorithms only release 1 dummy entries when new_mem_used < 3/4 * cache_allocated_size_ and cache_allocated_size_ - kSizeDummyEntry > new_mem_used. Now, the algorithms loop-releases as many dummy entries as possible when new_mem_used < 3/4 * cache_allocated_size_. - Updated WriteBufferManager's test cases to adapt to changes on the release algorithm mentioned above and left comment for some test cases for clarity - Replaced the previous cache key prefix generation (utilizing object address related to the cache client) with one that utilizes Cache->NewID() to prevent cache-key collision among dummy entry clients sharing the same cache. The specific collision we are preventing happens when the object address is reused for a new cache-key prefix while the old cache-key using that same object address in its prefix still exists in the cache. This could happen due to that, under LRU cache policy, there is a possible delay in releasing a cache entry after the cache client object owning that cache entry get deallocated. In this case, the object address related to the cache client object can get reused for other client object to generate a new cache-key prefix. This prefix generation can be made obsolete after Peter's unification of all the code generating cache key, mentioned in https://github.com/facebook/rocksdb/pull/8506#discussion_r667265255 Pull Request resolved: https://github.com/facebook/rocksdb/pull/8506 Test Plan: - Passing the added unit tests cache_reservation_manager_test.cc - Passing existing and adjusted write_buffer_manager_test.cc Reviewed By: ajkr Differential Revision: D29644135 Pulled By: hx235 fbshipit-source-id: 0fc93fbfe4a40bb41be85c314f8f2bafa8b741f7
3 years ago
// 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.
#include "cache/cache_reservation_manager.h"
#include <cassert>
#include <cstddef>
#include <cstring>
#include <memory>
#include "cache/cache_entry_roles.h"
#include "rocksdb/cache.h"
#include "rocksdb/slice.h"
#include "rocksdb/status.h"
#include "table/block_based/block_based_table_reader.h"
#include "util/coding.h"
namespace ROCKSDB_NAMESPACE {
CacheReservationManager::CacheReservationManager(std::shared_ptr<Cache> cache,
bool delayed_decrease)
: delayed_decrease_(delayed_decrease), cache_allocated_size_(0) {
assert(cache != nullptr);
cache_ = cache;
std::memset(cache_key_, 0, kCacheKeyPrefixSize + kMaxVarint64Length);
EncodeVarint64(cache_key_, cache_->NewId());
}
CacheReservationManager::~CacheReservationManager() {
for (auto* handle : dummy_handles_) {
cache_->Release(handle, true);
}
}
template <CacheEntryRole R>
Status CacheReservationManager::UpdateCacheReservation(
std::size_t new_mem_used) {
std::size_t cur_cache_allocated_size =
cache_allocated_size_.load(std::memory_order_relaxed);
if (new_mem_used == cur_cache_allocated_size) {
return Status::OK();
} else if (new_mem_used > cur_cache_allocated_size) {
Status s = IncreaseCacheReservation<R>(new_mem_used);
return s;
} else {
// In delayed decrease mode, we don't decrease cache reservation
// untill the memory usage is less than 3/4 of what we reserve
// in the cache.
// We do this because
// (1) Dummy entry insertion is expensive in block cache
// (2) Delayed releasing previously inserted dummy entries can save such
// expensive dummy entry insertion on memory increase in the near future,
// which is likely to happen when the memory usage is greater than or equal
// to 3/4 of what we reserve
if (delayed_decrease_ && new_mem_used >= cur_cache_allocated_size / 4 * 3) {
return Status::OK();
} else {
Status s = DecreaseCacheReservation(new_mem_used);
return s;
}
}
}
// Explicitly instantiate templates for "CacheEntryRole" values we use.
// This makes it possible to keep the template definitions in the .cc file.
template Status CacheReservationManager::UpdateCacheReservation<
CacheEntryRole::kWriteBuffer>(std::size_t new_mem_used);
template Status CacheReservationManager::UpdateCacheReservation<
CacheEntryRole::kCompressionDictionaryBuildingBuffer>(
std::size_t new_mem_used);
Refactor WriteBufferManager::CacheRep into CacheReservationManager (#8506) Summary: Context: To help cap various memory usage by a single limit of the block cache capacity, we charge the memory usage through inserting/releasing dummy entries in the block cache. CacheReservationManager is such a class (non thread-safe) responsible for inserting/removing dummy entries to reserve cache space for memory used by the class user. - Refactored the inner private class CacheRep of WriteBufferManager into public CacheReservationManager class for reusability such as for https://github.com/facebook/rocksdb/pull/8428 - Encapsulated implementation details of cache key generation and dummy entries insertion/release in cache reservation as discussed in https://github.com/facebook/rocksdb/pull/8506#discussion_r666550838 - Consolidated increase/decrease cache reservation into one API - UpdateCacheReservation. - Adjusted the previous dummy entry release algorithm in decreasing cache reservation to be loop-releasing dummy entries to stay symmetric to dummy entry insertion algorithm - Made the previous dummy entry release algorithm in delayed decrease mode more aggressive for better decreasing cache reservation when memory used is less likely to increase back. Previously, the algorithms only release 1 dummy entries when new_mem_used < 3/4 * cache_allocated_size_ and cache_allocated_size_ - kSizeDummyEntry > new_mem_used. Now, the algorithms loop-releases as many dummy entries as possible when new_mem_used < 3/4 * cache_allocated_size_. - Updated WriteBufferManager's test cases to adapt to changes on the release algorithm mentioned above and left comment for some test cases for clarity - Replaced the previous cache key prefix generation (utilizing object address related to the cache client) with one that utilizes Cache->NewID() to prevent cache-key collision among dummy entry clients sharing the same cache. The specific collision we are preventing happens when the object address is reused for a new cache-key prefix while the old cache-key using that same object address in its prefix still exists in the cache. This could happen due to that, under LRU cache policy, there is a possible delay in releasing a cache entry after the cache client object owning that cache entry get deallocated. In this case, the object address related to the cache client object can get reused for other client object to generate a new cache-key prefix. This prefix generation can be made obsolete after Peter's unification of all the code generating cache key, mentioned in https://github.com/facebook/rocksdb/pull/8506#discussion_r667265255 Pull Request resolved: https://github.com/facebook/rocksdb/pull/8506 Test Plan: - Passing the added unit tests cache_reservation_manager_test.cc - Passing existing and adjusted write_buffer_manager_test.cc Reviewed By: ajkr Differential Revision: D29644135 Pulled By: hx235 fbshipit-source-id: 0fc93fbfe4a40bb41be85c314f8f2bafa8b741f7
3 years ago
// For cache reservation manager unit tests
template Status CacheReservationManager::UpdateCacheReservation<
CacheEntryRole::kMisc>(std::size_t new_mem_used);
template <CacheEntryRole R>
Status CacheReservationManager::IncreaseCacheReservation(
std::size_t new_mem_used) {
Status return_status = Status::OK();
while (new_mem_used > cache_allocated_size_.load(std::memory_order_relaxed)) {
Cache::Handle* handle = nullptr;
return_status = cache_->Insert(GetNextCacheKey(), nullptr, kSizeDummyEntry,
GetNoopDeleterForRole<R>(), &handle);
if (return_status != Status::OK()) {
return return_status;
}
dummy_handles_.push_back(handle);
cache_allocated_size_ += kSizeDummyEntry;
}
return return_status;
}
Status CacheReservationManager::DecreaseCacheReservation(
std::size_t new_mem_used) {
Status return_status = Status::OK();
// Decrease to the smallest multiple of kSizeDummyEntry that is greater than
// or equal to new_mem_used We do addition instead of new_mem_used <=
// cache_allocated_size_.load(std::memory_order_relaxed) - kSizeDummyEntry to
// avoid underflow of size_t when cache_allocated_size_ = 0
while (new_mem_used + kSizeDummyEntry <=
cache_allocated_size_.load(std::memory_order_relaxed)) {
assert(!dummy_handles_.empty());
auto* handle = dummy_handles_.back();
cache_->Release(handle, true);
dummy_handles_.pop_back();
cache_allocated_size_ -= kSizeDummyEntry;
}
return return_status;
}
std::size_t CacheReservationManager::GetTotalReservedCacheSize() {
return cache_allocated_size_.load(std::memory_order_relaxed);
}
Slice CacheReservationManager::GetNextCacheKey() {
// Calling this function will have the side-effect of changing the
// underlying cache_key_ that is shared among other keys generated from this
// fucntion. Therefore please make sure the previous keys are saved/copied
// before calling this function.
std::memset(cache_key_ + kCacheKeyPrefixSize, 0, kMaxVarint64Length);
char* end =
EncodeVarint64(cache_key_ + kCacheKeyPrefixSize, next_cache_key_id_++);
return Slice(cache_key_, static_cast<std::size_t>(end - cache_key_));
}
} // namespace ROCKSDB_NAMESPACE