Summary:
…ons (#4676)"
This reverts commit b32d087dbb
.
`MemoryAllocator` needs to be with `Cache`, since cache entry can
outlive DB and block based table. The cache needs to hold reference to
memory allocator when deleting cache entry.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4697
Differential Revision: D13133490
Pulled By: yiwu-arbug
fbshipit-source-id: 8ef7e8a51263bfd929f892fd062665ff4ce9ce5a
304 lines
10 KiB
C++
304 lines
10 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 <string>
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#include "cache/sharded_cache.h"
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#include "port/port.h"
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#include "util/autovector.h"
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namespace rocksdb {
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// LRU cache implementation
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// An entry is a variable length heap-allocated structure.
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// Entries are referenced by cache and/or by any external entity.
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// The cache keeps all its entries in table. Some elements
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// are also stored on LRU list.
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//
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// LRUHandle can be in these states:
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// 1. Referenced externally AND in hash table.
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// In that case the entry is *not* in the LRU. (refs > 1 && in_cache == true)
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// 2. Not referenced externally and in hash table. In that case the entry is
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// in the LRU and can be freed. (refs == 1 && in_cache == true)
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// 3. Referenced externally and not in hash table. In that case the entry is
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// in not on LRU and not in table. (refs >= 1 && in_cache == false)
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//
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// All newly created LRUHandles are in state 1. If you call
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// LRUCacheShard::Release
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// on entry in state 1, it will go into state 2. To move from state 1 to
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// state 3, either call LRUCacheShard::Erase or LRUCacheShard::Insert with the
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// same key.
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// To move from state 2 to state 1, use LRUCacheShard::Lookup.
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// Before destruction, make sure that no handles are in state 1. This means
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// that any successful LRUCacheShard::Lookup/LRUCacheShard::Insert have a
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// matching
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// RUCache::Release (to move into state 2) or LRUCacheShard::Erase (for state 3)
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struct LRUHandle {
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void* value;
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void (*deleter)(const Slice&, void* value);
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LRUHandle* next_hash;
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LRUHandle* next;
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LRUHandle* prev;
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size_t charge; // TODO(opt): Only allow uint32_t?
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size_t key_length;
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uint32_t refs; // a number of refs to this entry
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// cache itself is counted as 1
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// Include the following flags:
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// in_cache: whether this entry is referenced by the hash table.
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// is_high_pri: whether this entry is high priority entry.
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// in_high_pri_pool: whether this entry is in high-pri pool.
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char flags;
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uint32_t hash; // Hash of key(); used for fast sharding and comparisons
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char key_data[1]; // Beginning of key
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Slice key() const {
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// For cheaper lookups, we allow a temporary Handle object
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// to store a pointer to a key in "value".
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if (next == this) {
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return *(reinterpret_cast<Slice*>(value));
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} else {
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return Slice(key_data, key_length);
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}
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}
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bool InCache() { return flags & 1; }
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bool IsHighPri() { return flags & 2; }
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bool InHighPriPool() { return flags & 4; }
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bool HasHit() { return flags & 8; }
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void SetInCache(bool in_cache) {
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if (in_cache) {
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flags |= 1;
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} else {
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flags &= ~1;
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}
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}
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void SetPriority(Cache::Priority priority) {
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if (priority == Cache::Priority::HIGH) {
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flags |= 2;
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} else {
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flags &= ~2;
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}
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}
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void SetInHighPriPool(bool in_high_pri_pool) {
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if (in_high_pri_pool) {
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flags |= 4;
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} else {
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flags &= ~4;
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}
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}
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void SetHit() { flags |= 8; }
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void Free() {
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assert((refs == 1 && InCache()) || (refs == 0 && !InCache()));
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if (deleter) {
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(*deleter)(key(), value);
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}
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delete[] reinterpret_cast<char*>(this);
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}
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};
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// We provide our own simple hash table since it removes a whole bunch
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// of porting hacks and is also faster than some of the built-in hash
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// table implementations in some of the compiler/runtime combinations
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// we have tested. E.g., readrandom speeds up by ~5% over the g++
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// 4.4.3's builtin hashtable.
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class LRUHandleTable {
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public:
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LRUHandleTable();
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~LRUHandleTable();
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LRUHandle* Lookup(const Slice& key, uint32_t hash);
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LRUHandle* Insert(LRUHandle* h);
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LRUHandle* Remove(const Slice& key, uint32_t hash);
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template <typename T>
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void ApplyToAllCacheEntries(T func) {
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for (uint32_t i = 0; i < length_; i++) {
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LRUHandle* h = list_[i];
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while (h != nullptr) {
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auto n = h->next_hash;
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assert(h->InCache());
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func(h);
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h = n;
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}
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}
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}
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private:
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// Return a pointer to slot that points to a cache entry that
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// matches key/hash. If there is no such cache entry, return a
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// pointer to the trailing slot in the corresponding linked list.
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LRUHandle** FindPointer(const Slice& key, uint32_t hash);
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void Resize();
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// The table consists of an array of buckets where each bucket is
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// a linked list of cache entries that hash into the bucket.
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LRUHandle** list_;
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uint32_t length_;
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uint32_t elems_;
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};
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// A single shard of sharded cache.
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class ALIGN_AS(CACHE_LINE_SIZE) LRUCacheShard : public CacheShard {
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public:
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LRUCacheShard(size_t capacity, bool strict_capacity_limit,
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double high_pri_pool_ratio);
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virtual ~LRUCacheShard();
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// Separate from constructor so caller can easily make an array of LRUCache
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// if current usage is more than new capacity, the function will attempt to
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// free the needed space
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virtual void SetCapacity(size_t capacity) override;
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// Set the flag to reject insertion if cache if full.
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virtual void SetStrictCapacityLimit(bool strict_capacity_limit) override;
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// Set percentage of capacity reserved for high-pri cache entries.
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void SetHighPriorityPoolRatio(double high_pri_pool_ratio);
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// Like Cache methods, but with an extra "hash" parameter.
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virtual Status Insert(const Slice& key, uint32_t hash, void* value,
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size_t charge,
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void (*deleter)(const Slice& key, void* value),
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Cache::Handle** handle,
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Cache::Priority priority) override;
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virtual Cache::Handle* Lookup(const Slice& key, uint32_t hash) override;
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virtual bool Ref(Cache::Handle* handle) override;
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virtual bool Release(Cache::Handle* handle,
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bool force_erase = false) override;
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virtual void Erase(const Slice& key, uint32_t hash) override;
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// Although in some platforms the update of size_t is atomic, to make sure
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// GetUsage() and GetPinnedUsage() work correctly under any platform, we'll
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// protect them with mutex_.
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virtual size_t GetUsage() const override;
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virtual size_t GetPinnedUsage() const override;
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virtual void ApplyToAllCacheEntries(void (*callback)(void*, size_t),
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bool thread_safe) override;
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virtual void EraseUnRefEntries() override;
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virtual std::string GetPrintableOptions() const override;
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void TEST_GetLRUList(LRUHandle** lru, LRUHandle** lru_low_pri);
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// Retrieves number of elements in LRU, for unit test purpose only
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// not threadsafe
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size_t TEST_GetLRUSize();
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// Retrives high pri pool ratio
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double GetHighPriPoolRatio();
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private:
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void LRU_Remove(LRUHandle* e);
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void LRU_Insert(LRUHandle* e);
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// Overflow the last entry in high-pri pool to low-pri pool until size of
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// high-pri pool is no larger than the size specify by high_pri_pool_pct.
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void MaintainPoolSize();
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// Just reduce the reference count by 1.
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// Return true if last reference
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bool Unref(LRUHandle* e);
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// Free some space following strict LRU policy until enough space
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// to hold (usage_ + charge) is freed or the lru list is empty
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// This function is not thread safe - it needs to be executed while
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// holding the mutex_
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void EvictFromLRU(size_t charge, autovector<LRUHandle*>* deleted);
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// Initialized before use.
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size_t capacity_;
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// Memory size for entries in high-pri pool.
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size_t high_pri_pool_usage_;
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// Whether to reject insertion if cache reaches its full capacity.
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bool strict_capacity_limit_;
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// Ratio of capacity reserved for high priority cache entries.
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double high_pri_pool_ratio_;
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// High-pri pool size, equals to capacity * high_pri_pool_ratio.
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// Remember the value to avoid recomputing each time.
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double high_pri_pool_capacity_;
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// Dummy head of LRU list.
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// lru.prev is newest entry, lru.next is oldest entry.
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// LRU contains items which can be evicted, ie reference only by cache
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LRUHandle lru_;
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// Pointer to head of low-pri pool in LRU list.
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LRUHandle* lru_low_pri_;
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// ------------^^^^^^^^^^^^^-----------
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// Not frequently modified data members
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// ------------------------------------
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//
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// We separate data members that are updated frequently from the ones that
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// are not frequently updated so that they don't share the same cache line
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// which will lead into false cache sharing
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//
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// ------------------------------------
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// Frequently modified data members
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// ------------vvvvvvvvvvvvv-----------
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LRUHandleTable table_;
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// Memory size for entries residing in the cache
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size_t usage_;
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// Memory size for entries residing only in the LRU list
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size_t lru_usage_;
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// mutex_ protects the following state.
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// We don't count mutex_ as the cache's internal state so semantically we
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// don't mind mutex_ invoking the non-const actions.
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mutable port::Mutex mutex_;
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};
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class LRUCache : public ShardedCache {
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public:
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LRUCache(size_t capacity, int num_shard_bits, bool strict_capacity_limit,
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double high_pri_pool_ratio,
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std::shared_ptr<MemoryAllocator> memory_allocator = nullptr);
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virtual ~LRUCache();
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virtual const char* Name() const override { return "LRUCache"; }
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virtual CacheShard* GetShard(int shard) override;
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virtual const CacheShard* GetShard(int shard) const override;
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virtual void* Value(Handle* handle) override;
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virtual size_t GetCharge(Handle* handle) const override;
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virtual uint32_t GetHash(Handle* handle) const override;
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virtual void DisownData() override;
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// Retrieves number of elements in LRU, for unit test purpose only
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size_t TEST_GetLRUSize();
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// Retrives high pri pool ratio
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double GetHighPriPoolRatio();
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private:
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LRUCacheShard* shards_ = nullptr;
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int num_shards_ = 0;
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};
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} // namespace rocksdb
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