Summary:
This reverts the previous commit 1d7048c598
, which broke the build.
Did a `git revert 1d7048c`.
Closes https://github.com/facebook/rocksdb/pull/2627
Differential Revision: D5476473
Pulled By: sagar0
fbshipit-source-id: 4756ff5c0dfc88c17eceb00e02c36176de728d06
725 lines
26 KiB
C++
725 lines
26 KiB
C++
// 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/clock_cache.h"
|
|
|
|
#ifndef SUPPORT_CLOCK_CACHE
|
|
|
|
namespace rocksdb {
|
|
|
|
std::shared_ptr<Cache> NewClockCache(size_t capacity, int num_shard_bits,
|
|
bool strict_capacity_limit) {
|
|
// Clock cache not supported.
|
|
return nullptr;
|
|
}
|
|
|
|
} // namespace rocksdb
|
|
|
|
#else
|
|
|
|
#include <assert.h>
|
|
#include <atomic>
|
|
#include <deque>
|
|
|
|
#include "tbb/concurrent_hash_map.h"
|
|
|
|
#include "cache/sharded_cache.h"
|
|
#include "port/port.h"
|
|
#include "util/autovector.h"
|
|
#include "util/mutexlock.h"
|
|
|
|
namespace rocksdb {
|
|
|
|
namespace {
|
|
|
|
// An implementation of the Cache interface based on CLOCK algorithm, with
|
|
// better concurrent performance than LRUCache. The idea of CLOCK algorithm
|
|
// is to maintain all cache entries in a circular list, and an iterator
|
|
// (the "head") pointing to the last examined entry. Eviction starts from the
|
|
// current head. Each entry is given a second chance before eviction, if it
|
|
// has been access since last examine. In contrast to LRU, no modification
|
|
// to the internal data-structure (except for flipping the usage bit) needs
|
|
// to be done upon lookup. This gives us oppertunity to implement a cache
|
|
// with better concurrency.
|
|
//
|
|
// Each cache entry is represented by a cache handle, and all the handles
|
|
// are arranged in a circular list, as describe above. Upon erase of an entry,
|
|
// we never remove the handle. Instead, the handle is put into a recycle bin
|
|
// to be re-use. This is to avoid memory dealocation, which is hard to deal
|
|
// with in concurrent environment.
|
|
//
|
|
// The cache also maintains a concurrent hash map for lookup. Any concurrent
|
|
// hash map implementation should do the work. We currently use
|
|
// tbb::concurrent_hash_map because it supports concurrent erase.
|
|
//
|
|
// Each cache handle has the following flags and counters, which are squeeze
|
|
// in an atomic interger, to make sure the handle always be in a consistent
|
|
// state:
|
|
//
|
|
// * In-cache bit: whether the entry is reference by the cache itself. If
|
|
// an entry is in cache, its key would also be available in the hash map.
|
|
// * Usage bit: whether the entry has been access by user since last
|
|
// examine for eviction. Can be reset by eviction.
|
|
// * Reference count: reference count by user.
|
|
//
|
|
// An entry can be reference only when it's in cache. An entry can be evicted
|
|
// only when it is in cache, has no usage since last examine, and reference
|
|
// count is zero.
|
|
//
|
|
// The follow figure shows a possible layout of the cache. Boxes represents
|
|
// cache handles and numbers in each box being in-cache bit, usage bit and
|
|
// reference count respectively.
|
|
//
|
|
// hash map:
|
|
// +-------+--------+
|
|
// | key | handle |
|
|
// +-------+--------+
|
|
// | "foo" | 5 |-------------------------------------+
|
|
// +-------+--------+ |
|
|
// | "bar" | 2 |--+ |
|
|
// +-------+--------+ | |
|
|
// | |
|
|
// head | |
|
|
// | | |
|
|
// circular list: | | |
|
|
// +-------+ +-------+ +-------+ +-------+ +-------+ +-------
|
|
// |(0,0,0)|---|(1,1,0)|---|(0,0,0)|---|(0,1,3)|---|(1,0,0)|---| ...
|
|
// +-------+ +-------+ +-------+ +-------+ +-------+ +-------
|
|
// | |
|
|
// +-------+ +-----------+
|
|
// | |
|
|
// +---+---+
|
|
// recycle bin: | 1 | 3 |
|
|
// +---+---+
|
|
//
|
|
// Suppose we try to insert "baz" into the cache at this point and the cache is
|
|
// full. The cache will first look for entries to evict, starting from where
|
|
// head points to (the second entry). It resets usage bit of the second entry,
|
|
// skips the third and fourth entry since they are not in cache, and finally
|
|
// evict the fifth entry ("foo"). It looks at recycle bin for available handle,
|
|
// grabs handle 3, and insert the key into the handle. The following figure
|
|
// shows the resulting layout.
|
|
//
|
|
// hash map:
|
|
// +-------+--------+
|
|
// | key | handle |
|
|
// +-------+--------+
|
|
// | "baz" | 3 |-------------+
|
|
// +-------+--------+ |
|
|
// | "bar" | 2 |--+ |
|
|
// +-------+--------+ | |
|
|
// | |
|
|
// | | head
|
|
// | | |
|
|
// circular list: | | |
|
|
// +-------+ +-------+ +-------+ +-------+ +-------+ +-------
|
|
// |(0,0,0)|---|(1,0,0)|---|(1,0,0)|---|(0,1,3)|---|(0,0,0)|---| ...
|
|
// +-------+ +-------+ +-------+ +-------+ +-------+ +-------
|
|
// | |
|
|
// +-------+ +-----------------------------------+
|
|
// | |
|
|
// +---+---+
|
|
// recycle bin: | 1 | 5 |
|
|
// +---+---+
|
|
//
|
|
// A global mutex guards the circular list, the head, and the recycle bin.
|
|
// We additionally require that modifying the hash map needs to hold the mutex.
|
|
// As such, Modifying the cache (such as Insert() and Erase()) require to
|
|
// hold the mutex. Lookup() only access the hash map and the flags associated
|
|
// with each handle, and don't require explicit locking. Release() has to
|
|
// acquire the mutex only when it releases the last reference to the entry and
|
|
// the entry has been erased from cache explicitly. A future improvement could
|
|
// be to remove the mutex completely.
|
|
//
|
|
// Benchmark:
|
|
// We run readrandom db_bench on a test DB of size 13GB, with size of each
|
|
// level:
|
|
//
|
|
// Level Files Size(MB)
|
|
// -------------------------
|
|
// L0 1 0.01
|
|
// L1 18 17.32
|
|
// L2 230 182.94
|
|
// L3 1186 1833.63
|
|
// L4 4602 8140.30
|
|
//
|
|
// We test with both 32 and 16 read threads, with 2GB cache size (the whole DB
|
|
// doesn't fits in) and 64GB cache size (the whole DB can fit in cache), and
|
|
// whether to put index and filter blocks in block cache. The benchmark runs
|
|
// with
|
|
// with RocksDB 4.10. We got the following result:
|
|
//
|
|
// Threads Cache Cache ClockCache LRUCache
|
|
// Size Index/Filter Throughput(MB/s) Hit Throughput(MB/s) Hit
|
|
// 32 2GB yes 466.7 85.9% 433.7 86.5%
|
|
// 32 2GB no 529.9 72.7% 532.7 73.9%
|
|
// 32 64GB yes 649.9 99.9% 507.9 99.9%
|
|
// 32 64GB no 740.4 99.9% 662.8 99.9%
|
|
// 16 2GB yes 278.4 85.9% 283.4 86.5%
|
|
// 16 2GB no 318.6 72.7% 335.8 73.9%
|
|
// 16 64GB yes 391.9 99.9% 353.3 99.9%
|
|
// 16 64GB no 433.8 99.8% 419.4 99.8%
|
|
|
|
// Cache entry meta data.
|
|
struct CacheHandle {
|
|
Slice key;
|
|
uint32_t hash;
|
|
void* value;
|
|
size_t charge;
|
|
void (*deleter)(const Slice&, void* value);
|
|
|
|
// Flags and counters associated with the cache handle:
|
|
// lowest bit: n-cache bit
|
|
// second lowest bit: usage bit
|
|
// the rest bits: reference count
|
|
// The handle is unused when flags equals to 0. The thread decreases the count
|
|
// to 0 is responsible to put the handle back to recycle_ and cleanup memory.
|
|
std::atomic<uint32_t> flags;
|
|
|
|
CacheHandle() = default;
|
|
|
|
CacheHandle(const CacheHandle& a) { *this = a; }
|
|
|
|
CacheHandle(const Slice& k, void* v,
|
|
void (*del)(const Slice& key, void* value))
|
|
: key(k), value(v), deleter(del) {}
|
|
|
|
CacheHandle& operator=(const CacheHandle& a) {
|
|
// Only copy members needed for deletion.
|
|
key = a.key;
|
|
value = a.value;
|
|
deleter = a.deleter;
|
|
return *this;
|
|
}
|
|
};
|
|
|
|
// Key of hash map. We store hash value with the key for convenience.
|
|
struct CacheKey {
|
|
Slice key;
|
|
uint32_t hash_value;
|
|
|
|
CacheKey() = default;
|
|
|
|
CacheKey(const Slice& k, uint32_t h) {
|
|
key = k;
|
|
hash_value = h;
|
|
}
|
|
|
|
static bool equal(const CacheKey& a, const CacheKey& b) {
|
|
return a.hash_value == b.hash_value && a.key == b.key;
|
|
}
|
|
|
|
static size_t hash(const CacheKey& a) {
|
|
return static_cast<size_t>(a.hash_value);
|
|
}
|
|
};
|
|
|
|
struct CleanupContext {
|
|
// List of values to be deleted, along with the key and deleter.
|
|
autovector<CacheHandle> to_delete_value;
|
|
|
|
// List of keys to be deleted.
|
|
autovector<const char*> to_delete_key;
|
|
};
|
|
|
|
// A cache shard which maintains its own CLOCK cache.
|
|
class ClockCacheShard : public CacheShard {
|
|
public:
|
|
// Hash map type.
|
|
typedef tbb::concurrent_hash_map<CacheKey, CacheHandle*, CacheKey> HashTable;
|
|
|
|
ClockCacheShard();
|
|
~ClockCacheShard();
|
|
|
|
// Interfaces
|
|
virtual void SetCapacity(size_t capacity) override;
|
|
virtual void SetStrictCapacityLimit(bool strict_capacity_limit) override;
|
|
virtual Status Insert(const Slice& key, uint32_t hash, void* value,
|
|
size_t charge,
|
|
void (*deleter)(const Slice& key, void* value),
|
|
Cache::Handle** handle,
|
|
Cache::Priority priority) override;
|
|
virtual Cache::Handle* Lookup(const Slice& key, uint32_t hash) override;
|
|
// If the entry in in cache, increase reference count and return true.
|
|
// Return false otherwise.
|
|
//
|
|
// Not necessary to hold mutex_ before being called.
|
|
virtual bool Ref(Cache::Handle* handle) override;
|
|
virtual bool Release(Cache::Handle* handle,
|
|
bool force_erase = false) override;
|
|
virtual void Erase(const Slice& key, uint32_t hash) override;
|
|
bool EraseAndConfirm(const Slice& key, uint32_t hash,
|
|
CleanupContext* context);
|
|
virtual size_t GetUsage() const override;
|
|
virtual size_t GetPinnedUsage() const override;
|
|
virtual void EraseUnRefEntries() override;
|
|
virtual void ApplyToAllCacheEntries(void (*callback)(void*, size_t),
|
|
bool thread_safe) override;
|
|
|
|
private:
|
|
static const uint32_t kInCacheBit = 1;
|
|
static const uint32_t kUsageBit = 2;
|
|
static const uint32_t kRefsOffset = 2;
|
|
static const uint32_t kOneRef = 1 << kRefsOffset;
|
|
|
|
// Helper functions to extract cache handle flags and counters.
|
|
static bool InCache(uint32_t flags) { return flags & kInCacheBit; }
|
|
static bool HasUsage(uint32_t flags) { return flags & kUsageBit; }
|
|
static uint32_t CountRefs(uint32_t flags) { return flags >> kRefsOffset; }
|
|
|
|
// Decrease reference count of the entry. If this decreases the count to 0,
|
|
// recycle the entry. If set_usage is true, also set the usage bit.
|
|
//
|
|
// returns true if a value is erased.
|
|
//
|
|
// Not necessary to hold mutex_ before being called.
|
|
bool Unref(CacheHandle* handle, bool set_usage, CleanupContext* context);
|
|
|
|
// Unset in-cache bit of the entry. Recycle the handle if necessary.
|
|
//
|
|
// returns true if a value is erased.
|
|
//
|
|
// Has to hold mutex_ before being called.
|
|
bool UnsetInCache(CacheHandle* handle, CleanupContext* context);
|
|
|
|
// Put the handle back to recycle_ list, and put the value associated with
|
|
// it into to-be-deleted list. It doesn't cleanup the key as it might be
|
|
// reused by another handle.
|
|
//
|
|
// Has to hold mutex_ before being called.
|
|
void RecycleHandle(CacheHandle* handle, CleanupContext* context);
|
|
|
|
// Delete keys and values in to-be-deleted list. Call the method without
|
|
// holding mutex, as destructors can be expensive.
|
|
void Cleanup(const CleanupContext& context);
|
|
|
|
// Examine the handle for eviction. If the handle is in cache, usage bit is
|
|
// not set, and referece count is 0, evict it from cache. Otherwise unset
|
|
// the usage bit.
|
|
//
|
|
// Has to hold mutex_ before being called.
|
|
bool TryEvict(CacheHandle* value, CleanupContext* context);
|
|
|
|
// Scan through the circular list, evict entries until we get enough capacity
|
|
// for new cache entry of specific size. Return true if success, false
|
|
// otherwise.
|
|
//
|
|
// Has to hold mutex_ before being called.
|
|
bool EvictFromCache(size_t charge, CleanupContext* context);
|
|
|
|
CacheHandle* Insert(const Slice& key, uint32_t hash, void* value,
|
|
size_t change,
|
|
void (*deleter)(const Slice& key, void* value),
|
|
bool hold_reference, CleanupContext* context);
|
|
|
|
// Guards list_, head_, and recycle_. In addition, updating table_ also has
|
|
// to hold the mutex, to avoid the cache being in inconsistent state.
|
|
mutable port::Mutex mutex_;
|
|
|
|
// The circular list of cache handles. Initially the list is empty. Once a
|
|
// handle is needed by insertion, and no more handles are available in
|
|
// recycle bin, one more handle is appended to the end.
|
|
//
|
|
// We use std::deque for the circular list because we want to make sure
|
|
// pointers to handles are valid through out the life-cycle of the cache
|
|
// (in contrast to std::vector), and be able to grow the list (in contrast
|
|
// to statically allocated arrays).
|
|
std::deque<CacheHandle> list_;
|
|
|
|
// Pointer to the next handle in the circular list to be examine for
|
|
// eviction.
|
|
size_t head_;
|
|
|
|
// Recycle bin of cache handles.
|
|
autovector<CacheHandle*> recycle_;
|
|
|
|
// Maximum cache size.
|
|
std::atomic<size_t> capacity_;
|
|
|
|
// Current total size of the cache.
|
|
std::atomic<size_t> usage_;
|
|
|
|
// Total un-released cache size.
|
|
std::atomic<size_t> pinned_usage_;
|
|
|
|
// Whether allow insert into cache if cache is full.
|
|
std::atomic<bool> strict_capacity_limit_;
|
|
|
|
// Hash table (tbb::concurrent_hash_map) for lookup.
|
|
HashTable table_;
|
|
};
|
|
|
|
ClockCacheShard::ClockCacheShard()
|
|
: head_(0), usage_(0), pinned_usage_(0), strict_capacity_limit_(false) {}
|
|
|
|
ClockCacheShard::~ClockCacheShard() {
|
|
for (auto& handle : list_) {
|
|
uint32_t flags = handle.flags.load(std::memory_order_relaxed);
|
|
if (InCache(flags) || CountRefs(flags) > 0) {
|
|
(*handle.deleter)(handle.key, handle.value);
|
|
delete[] handle.key.data();
|
|
}
|
|
}
|
|
}
|
|
|
|
size_t ClockCacheShard::GetUsage() const {
|
|
return usage_.load(std::memory_order_relaxed);
|
|
}
|
|
|
|
size_t ClockCacheShard::GetPinnedUsage() const {
|
|
return pinned_usage_.load(std::memory_order_relaxed);
|
|
}
|
|
|
|
void ClockCacheShard::ApplyToAllCacheEntries(void (*callback)(void*, size_t),
|
|
bool thread_safe) {
|
|
if (thread_safe) {
|
|
mutex_.Lock();
|
|
}
|
|
for (auto& handle : list_) {
|
|
// Use relaxed semantics instead of acquire semantics since we are either
|
|
// holding mutex, or don't have thread safe requirement.
|
|
uint32_t flags = handle.flags.load(std::memory_order_relaxed);
|
|
if (InCache(flags)) {
|
|
callback(handle.value, handle.charge);
|
|
}
|
|
}
|
|
if (thread_safe) {
|
|
mutex_.Unlock();
|
|
}
|
|
}
|
|
|
|
void ClockCacheShard::RecycleHandle(CacheHandle* handle,
|
|
CleanupContext* context) {
|
|
mutex_.AssertHeld();
|
|
assert(!InCache(handle->flags) && CountRefs(handle->flags) == 0);
|
|
context->to_delete_key.push_back(handle->key.data());
|
|
context->to_delete_value.emplace_back(*handle);
|
|
handle->key.clear();
|
|
handle->value = nullptr;
|
|
handle->deleter = nullptr;
|
|
recycle_.push_back(handle);
|
|
usage_.fetch_sub(handle->charge, std::memory_order_relaxed);
|
|
}
|
|
|
|
void ClockCacheShard::Cleanup(const CleanupContext& context) {
|
|
for (const CacheHandle& handle : context.to_delete_value) {
|
|
if (handle.deleter) {
|
|
(*handle.deleter)(handle.key, handle.value);
|
|
}
|
|
}
|
|
for (const char* key : context.to_delete_key) {
|
|
delete[] key;
|
|
}
|
|
}
|
|
|
|
bool ClockCacheShard::Ref(Cache::Handle* h) {
|
|
auto handle = reinterpret_cast<CacheHandle*>(h);
|
|
// CAS loop to increase reference count.
|
|
uint32_t flags = handle->flags.load(std::memory_order_relaxed);
|
|
while (InCache(flags)) {
|
|
// Use acquire semantics on success, as further operations on the cache
|
|
// entry has to be order after reference count is increased.
|
|
if (handle->flags.compare_exchange_weak(flags, flags + kOneRef,
|
|
std::memory_order_acquire,
|
|
std::memory_order_relaxed)) {
|
|
if (CountRefs(flags) == 0) {
|
|
// No reference count before the operation.
|
|
pinned_usage_.fetch_add(handle->charge, std::memory_order_relaxed);
|
|
}
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
bool ClockCacheShard::Unref(CacheHandle* handle, bool set_usage,
|
|
CleanupContext* context) {
|
|
if (set_usage) {
|
|
handle->flags.fetch_or(kUsageBit, std::memory_order_relaxed);
|
|
}
|
|
// Use acquire-release semantics as previous operations on the cache entry
|
|
// has to be order before reference count is decreased, and potential cleanup
|
|
// of the entry has to be order after.
|
|
uint32_t flags = handle->flags.fetch_sub(kOneRef, std::memory_order_acq_rel);
|
|
assert(CountRefs(flags) > 0);
|
|
if (CountRefs(flags) == 1) {
|
|
// this is the last reference.
|
|
pinned_usage_.fetch_sub(handle->charge, std::memory_order_relaxed);
|
|
// Cleanup if it is the last reference.
|
|
if (!InCache(flags)) {
|
|
MutexLock l(&mutex_);
|
|
RecycleHandle(handle, context);
|
|
}
|
|
}
|
|
return context->to_delete_value.size();
|
|
}
|
|
|
|
bool ClockCacheShard::UnsetInCache(CacheHandle* handle,
|
|
CleanupContext* context) {
|
|
mutex_.AssertHeld();
|
|
// Use acquire-release semantics as previous operations on the cache entry
|
|
// has to be order before reference count is decreased, and potential cleanup
|
|
// of the entry has to be order after.
|
|
uint32_t flags =
|
|
handle->flags.fetch_and(~kInCacheBit, std::memory_order_acq_rel);
|
|
// Cleanup if it is the last reference.
|
|
if (InCache(flags) && CountRefs(flags) == 0) {
|
|
RecycleHandle(handle, context);
|
|
}
|
|
return context->to_delete_value.size();
|
|
}
|
|
|
|
bool ClockCacheShard::TryEvict(CacheHandle* handle, CleanupContext* context) {
|
|
mutex_.AssertHeld();
|
|
uint32_t flags = kInCacheBit;
|
|
if (handle->flags.compare_exchange_strong(flags, 0, std::memory_order_acquire,
|
|
std::memory_order_relaxed)) {
|
|
bool erased __attribute__((__unused__)) =
|
|
table_.erase(CacheKey(handle->key, handle->hash));
|
|
assert(erased);
|
|
RecycleHandle(handle, context);
|
|
return true;
|
|
}
|
|
handle->flags.fetch_and(~kUsageBit, std::memory_order_relaxed);
|
|
return false;
|
|
}
|
|
|
|
bool ClockCacheShard::EvictFromCache(size_t charge, CleanupContext* context) {
|
|
size_t usage = usage_.load(std::memory_order_relaxed);
|
|
size_t capacity = capacity_.load(std::memory_order_relaxed);
|
|
if (usage == 0) {
|
|
return charge <= capacity;
|
|
}
|
|
size_t new_head = head_;
|
|
bool second_iteration = false;
|
|
while (usage + charge > capacity) {
|
|
assert(new_head < list_.size());
|
|
if (TryEvict(&list_[new_head], context)) {
|
|
usage = usage_.load(std::memory_order_relaxed);
|
|
}
|
|
new_head = (new_head + 1 >= list_.size()) ? 0 : new_head + 1;
|
|
if (new_head == head_) {
|
|
if (second_iteration) {
|
|
return false;
|
|
} else {
|
|
second_iteration = true;
|
|
}
|
|
}
|
|
}
|
|
head_ = new_head;
|
|
return true;
|
|
}
|
|
|
|
void ClockCacheShard::SetCapacity(size_t capacity) {
|
|
CleanupContext context;
|
|
{
|
|
MutexLock l(&mutex_);
|
|
capacity_.store(capacity, std::memory_order_relaxed);
|
|
EvictFromCache(0, &context);
|
|
}
|
|
Cleanup(context);
|
|
}
|
|
|
|
void ClockCacheShard::SetStrictCapacityLimit(bool strict_capacity_limit) {
|
|
strict_capacity_limit_.store(strict_capacity_limit,
|
|
std::memory_order_relaxed);
|
|
}
|
|
|
|
CacheHandle* ClockCacheShard::Insert(
|
|
const Slice& key, uint32_t hash, void* value, size_t charge,
|
|
void (*deleter)(const Slice& key, void* value), bool hold_reference,
|
|
CleanupContext* context) {
|
|
MutexLock l(&mutex_);
|
|
bool success = EvictFromCache(charge, context);
|
|
bool strict = strict_capacity_limit_.load(std::memory_order_relaxed);
|
|
if (!success && (strict || !hold_reference)) {
|
|
context->to_delete_key.push_back(key.data());
|
|
if (!hold_reference) {
|
|
context->to_delete_value.emplace_back(key, value, deleter);
|
|
}
|
|
return nullptr;
|
|
}
|
|
// Grab available handle from recycle bin. If recycle bin is empty, create
|
|
// and append new handle to end of circular list.
|
|
CacheHandle* handle = nullptr;
|
|
if (!recycle_.empty()) {
|
|
handle = recycle_.back();
|
|
recycle_.pop_back();
|
|
} else {
|
|
list_.emplace_back();
|
|
handle = &list_.back();
|
|
}
|
|
// Fill handle.
|
|
handle->key = key;
|
|
handle->hash = hash;
|
|
handle->value = value;
|
|
handle->charge = charge;
|
|
handle->deleter = deleter;
|
|
uint32_t flags = hold_reference ? kInCacheBit + kOneRef : kInCacheBit;
|
|
handle->flags.store(flags, std::memory_order_relaxed);
|
|
HashTable::accessor accessor;
|
|
if (table_.find(accessor, CacheKey(key, hash))) {
|
|
CacheHandle* existing_handle = accessor->second;
|
|
table_.erase(accessor);
|
|
UnsetInCache(existing_handle, context);
|
|
}
|
|
table_.insert(HashTable::value_type(CacheKey(key, hash), handle));
|
|
if (hold_reference) {
|
|
pinned_usage_.fetch_add(charge, std::memory_order_relaxed);
|
|
}
|
|
usage_.fetch_add(charge, std::memory_order_relaxed);
|
|
return handle;
|
|
}
|
|
|
|
Status ClockCacheShard::Insert(const Slice& key, uint32_t hash, void* value,
|
|
size_t charge,
|
|
void (*deleter)(const Slice& key, void* value),
|
|
Cache::Handle** out_handle,
|
|
Cache::Priority priority) {
|
|
CleanupContext context;
|
|
HashTable::accessor accessor;
|
|
char* key_data = new char[key.size()];
|
|
memcpy(key_data, key.data(), key.size());
|
|
Slice key_copy(key_data, key.size());
|
|
CacheHandle* handle = Insert(key_copy, hash, value, charge, deleter,
|
|
out_handle != nullptr, &context);
|
|
Status s;
|
|
if (out_handle != nullptr) {
|
|
if (handle == nullptr) {
|
|
s = Status::Incomplete("Insert failed due to LRU cache being full.");
|
|
} else {
|
|
*out_handle = reinterpret_cast<Cache::Handle*>(handle);
|
|
}
|
|
}
|
|
Cleanup(context);
|
|
return s;
|
|
}
|
|
|
|
Cache::Handle* ClockCacheShard::Lookup(const Slice& key, uint32_t hash) {
|
|
HashTable::const_accessor accessor;
|
|
if (!table_.find(accessor, CacheKey(key, hash))) {
|
|
return nullptr;
|
|
}
|
|
CacheHandle* handle = accessor->second;
|
|
accessor.release();
|
|
// Ref() could fail if another thread sneak in and evict/erase the cache
|
|
// entry before we are able to hold reference.
|
|
if (!Ref(reinterpret_cast<Cache::Handle*>(handle))) {
|
|
return nullptr;
|
|
}
|
|
// Double check the key since the handle may now representing another key
|
|
// if other threads sneak in, evict/erase the entry and re-used the handle
|
|
// for another cache entry.
|
|
if (hash != handle->hash || key != handle->key) {
|
|
CleanupContext context;
|
|
Unref(handle, false, &context);
|
|
// It is possible Unref() delete the entry, so we need to cleanup.
|
|
Cleanup(context);
|
|
return nullptr;
|
|
}
|
|
return reinterpret_cast<Cache::Handle*>(handle);
|
|
}
|
|
|
|
bool ClockCacheShard::Release(Cache::Handle* h, bool force_erase) {
|
|
CleanupContext context;
|
|
CacheHandle* handle = reinterpret_cast<CacheHandle*>(h);
|
|
bool erased = Unref(handle, true, &context);
|
|
if (force_erase && !erased) {
|
|
erased = EraseAndConfirm(handle->key, handle->hash, &context);
|
|
}
|
|
Cleanup(context);
|
|
return erased;
|
|
}
|
|
|
|
void ClockCacheShard::Erase(const Slice& key, uint32_t hash) {
|
|
CleanupContext context;
|
|
EraseAndConfirm(key, hash, &context);
|
|
Cleanup(context);
|
|
}
|
|
|
|
bool ClockCacheShard::EraseAndConfirm(const Slice& key, uint32_t hash,
|
|
CleanupContext* context) {
|
|
MutexLock l(&mutex_);
|
|
HashTable::accessor accessor;
|
|
bool erased = false;
|
|
if (table_.find(accessor, CacheKey(key, hash))) {
|
|
CacheHandle* handle = accessor->second;
|
|
table_.erase(accessor);
|
|
erased = UnsetInCache(handle, context);
|
|
}
|
|
return erased;
|
|
}
|
|
|
|
void ClockCacheShard::EraseUnRefEntries() {
|
|
CleanupContext context;
|
|
{
|
|
MutexLock l(&mutex_);
|
|
table_.clear();
|
|
for (auto& handle : list_) {
|
|
UnsetInCache(&handle, &context);
|
|
}
|
|
}
|
|
Cleanup(context);
|
|
}
|
|
|
|
class ClockCache : public ShardedCache {
|
|
public:
|
|
ClockCache(size_t capacity, int num_shard_bits, bool strict_capacity_limit)
|
|
: ShardedCache(capacity, num_shard_bits, strict_capacity_limit) {
|
|
int num_shards = 1 << num_shard_bits;
|
|
shards_ = new ClockCacheShard[num_shards];
|
|
SetCapacity(capacity);
|
|
SetStrictCapacityLimit(strict_capacity_limit);
|
|
}
|
|
|
|
virtual ~ClockCache() { delete[] shards_; }
|
|
|
|
virtual const char* Name() const override { return "ClockCache"; }
|
|
|
|
virtual CacheShard* GetShard(int shard) override {
|
|
return reinterpret_cast<CacheShard*>(&shards_[shard]);
|
|
}
|
|
|
|
virtual const CacheShard* GetShard(int shard) const override {
|
|
return reinterpret_cast<CacheShard*>(&shards_[shard]);
|
|
}
|
|
|
|
virtual void* Value(Handle* handle) override {
|
|
return reinterpret_cast<const CacheHandle*>(handle)->value;
|
|
}
|
|
|
|
virtual size_t GetCharge(Handle* handle) const override {
|
|
return reinterpret_cast<const CacheHandle*>(handle)->charge;
|
|
}
|
|
|
|
virtual uint32_t GetHash(Handle* handle) const override {
|
|
return reinterpret_cast<const CacheHandle*>(handle)->hash;
|
|
}
|
|
|
|
virtual void DisownData() override { shards_ = nullptr; }
|
|
|
|
private:
|
|
ClockCacheShard* shards_;
|
|
};
|
|
|
|
} // end anonymous namespace
|
|
|
|
std::shared_ptr<Cache> NewClockCache(size_t capacity, int num_shard_bits,
|
|
bool strict_capacity_limit) {
|
|
if (num_shard_bits < 0) {
|
|
num_shard_bits = GetDefaultCacheShardBits(capacity);
|
|
}
|
|
return std::make_shared<ClockCache>(capacity, num_shard_bits,
|
|
strict_capacity_limit);
|
|
}
|
|
|
|
} // namespace rocksdb
|
|
|
|
#endif // SUPPORT_CLOCK_CACHE
|