Revision faba3fb53defe4fa32f32202d459726ad49f4033 authored by Andrew Kryczka on 06 April 2018, 03:58:35 UTC, committed by Facebook Github Bot on 06 April 2018, 04:13:21 UTC
Summary: When `max_valid_backups_to_open` is set, the `BackupEngine` doesn't know about the files referenced by existing backups. This PR prevents us from deleting valid files when that option is set, in cases where we are unable to accurately determine refcount. There are warnings logged when we may miss deleting unreferenced files, and a recommendation in the header for users to periodically unset this option and run a full `GarbageCollect`. Closes https://github.com/facebook/rocksdb/pull/3518 Differential Revision: D7008331 Pulled By: ajkr fbshipit-source-id: 87907f964dc9716e229d08636a895d2fc7b72305
1 parent 6571770
write_buffer_manager.cc
// 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 "rocksdb/write_buffer_manager.h"
#include <mutex>
#include "util/coding.h"
namespace rocksdb {
#ifndef ROCKSDB_LITE
namespace {
const size_t kSizeDummyEntry = 1024 * 1024;
// The key will be longer than keys for blocks in SST files so they won't
// conflict.
const size_t kCacheKeyPrefix = kMaxVarint64Length * 4 + 1;
} // namespace
struct WriteBufferManager::CacheRep {
std::shared_ptr<Cache> cache_;
std::mutex cache_mutex_;
std::atomic<size_t> cache_allocated_size_;
// The non-prefix part will be updated according to the ID to use.
char cache_key_[kCacheKeyPrefix + kMaxVarint64Length];
uint64_t next_cache_key_id_ = 0;
std::vector<Cache::Handle*> dummy_handles_;
explicit CacheRep(std::shared_ptr<Cache> cache)
: cache_(cache), cache_allocated_size_(0) {
memset(cache_key_, 0, kCacheKeyPrefix);
size_t pointer_size = sizeof(const void*);
assert(pointer_size <= kCacheKeyPrefix);
memcpy(cache_key_, static_cast<const void*>(this), pointer_size);
}
Slice GetNextCacheKey() {
memset(cache_key_ + kCacheKeyPrefix, 0, kMaxVarint64Length);
char* end =
EncodeVarint64(cache_key_ + kCacheKeyPrefix, next_cache_key_id_++);
return Slice(cache_key_, static_cast<size_t>(end - cache_key_));
}
};
#else
struct WriteBufferManager::CacheRep {};
#endif // ROCKSDB_LITE
WriteBufferManager::WriteBufferManager(size_t _buffer_size,
std::shared_ptr<Cache> cache)
: buffer_size_(_buffer_size),
mutable_limit_(buffer_size_ * 7 / 8),
memory_used_(0),
memory_active_(0),
cache_rep_(nullptr) {
#ifndef ROCKSDB_LITE
if (cache) {
// Construct the cache key using the pointer to this.
cache_rep_.reset(new CacheRep(cache));
}
#endif // ROCKSDB_LITE
}
WriteBufferManager::~WriteBufferManager() {
#ifndef ROCKSDB_LITE
if (cache_rep_) {
for (auto* handle : cache_rep_->dummy_handles_) {
cache_rep_->cache_->Release(handle, true);
}
}
#endif // ROCKSDB_LITE
}
// Should only be called from write thread
void WriteBufferManager::ReserveMemWithCache(size_t mem) {
#ifndef ROCKSDB_LITE
assert(cache_rep_ != nullptr);
// Use a mutex to protect various data structures. Can be optimzied to a
// lock-free solution if it ends up with a performance bottleneck.
std::lock_guard<std::mutex> lock(cache_rep_->cache_mutex_);
size_t new_mem_used = memory_used_.load(std::memory_order_relaxed) + mem;
memory_used_.store(new_mem_used, std::memory_order_relaxed);
while (new_mem_used > cache_rep_->cache_allocated_size_) {
// Expand size by at least 1MB.
// Add a dummy record to the cache
Cache::Handle* handle;
cache_rep_->cache_->Insert(cache_rep_->GetNextCacheKey(), nullptr,
kSizeDummyEntry, nullptr, &handle);
cache_rep_->dummy_handles_.push_back(handle);
cache_rep_->cache_allocated_size_ += kSizeDummyEntry;
}
#endif // ROCKSDB_LITE
}
void WriteBufferManager::FreeMemWithCache(size_t mem) {
#ifndef ROCKSDB_LITE
assert(cache_rep_ != nullptr);
// Use a mutex to protect various data structures. Can be optimzied to a
// lock-free solution if it ends up with a performance bottleneck.
std::lock_guard<std::mutex> lock(cache_rep_->cache_mutex_);
size_t new_mem_used = memory_used_.load(std::memory_order_relaxed) - mem;
memory_used_.store(new_mem_used, std::memory_order_relaxed);
// Gradually shrink memory costed in the block cache if the actual
// usage is less than 3/4 of what we reserve from the block cache.
// We do this becausse:
// 1. we don't pay the cost of the block cache immediately a memtable is
// freed, as block cache insert is expensive;
// 2. eventually, if we walk away from a temporary memtable size increase,
// we make sure shrink the memory costed in block cache over time.
// In this way, we only shrink costed memory showly even there is enough
// margin.
if (new_mem_used < cache_rep_->cache_allocated_size_ / 4 * 3 &&
cache_rep_->cache_allocated_size_ - kSizeDummyEntry > new_mem_used) {
assert(!cache_rep_->dummy_handles_.empty());
cache_rep_->cache_->Release(cache_rep_->dummy_handles_.back(), true);
cache_rep_->dummy_handles_.pop_back();
cache_rep_->cache_allocated_size_ -= kSizeDummyEntry;
}
#endif // ROCKSDB_LITE
}
} // namespace rocksdb
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