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// 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).
#include "utilities/simulator_cache/cache_simulator.h"
#include <algorithm>
#include "db/dbformat.h"
#include "rocksdb/trace_record.h"
namespace ROCKSDB_NAMESPACE {
namespace {
const std::string kGhostCachePrefix = "ghost_";
} // namespace
GhostCache::GhostCache(std::shared_ptr<Cache> sim_cache)
: sim_cache_(sim_cache) {}
bool GhostCache::Admit(const Slice& lookup_key) {
auto handle = sim_cache_->Lookup(lookup_key);
if (handle != nullptr) {
sim_cache_->Release(handle);
return true;
}
// TODO: Should we check for errors here?
auto s = sim_cache_->Insert(lookup_key, /*obj=*/nullptr,
&kNoopCacheItemHelper, lookup_key.size());
s.PermitUncheckedError();
return false;
}
CacheSimulator::CacheSimulator(std::unique_ptr<GhostCache>&& ghost_cache,
std::shared_ptr<Cache> sim_cache)
: ghost_cache_(std::move(ghost_cache)), sim_cache_(sim_cache) {}
void CacheSimulator::Access(const BlockCacheTraceRecord& access) {
bool admit = true;
const bool is_user_access =
BlockCacheTraceHelper::IsUserAccess(access.caller);
bool is_cache_miss = true;
if (ghost_cache_ && !access.no_insert) {
admit = ghost_cache_->Admit(access.block_key);
}
auto handle = sim_cache_->Lookup(access.block_key);
if (handle != nullptr) {
sim_cache_->Release(handle);
is_cache_miss = false;
} else {
if (!access.no_insert && admit && access.block_size > 0) {
// Ignore errors on insert
auto s = sim_cache_->Insert(access.block_key, /*obj=*/nullptr,
&kNoopCacheItemHelper, access.block_size);
s.PermitUncheckedError();
}
}
miss_ratio_stats_.UpdateMetrics(access.access_timestamp, is_user_access,
is_cache_miss);
}
void MissRatioStats::UpdateMetrics(uint64_t timestamp_in_ms,
bool is_user_access, bool is_cache_miss) {
uint64_t timestamp_in_seconds = timestamp_in_ms / kMicrosInSecond;
num_accesses_timeline_[timestamp_in_seconds] += 1;
num_accesses_ += 1;
if (num_misses_timeline_.find(timestamp_in_seconds) ==
num_misses_timeline_.end()) {
num_misses_timeline_[timestamp_in_seconds] = 0;
}
if (is_cache_miss) {
num_misses_ += 1;
num_misses_timeline_[timestamp_in_seconds] += 1;
}
if (is_user_access) {
user_accesses_ += 1;
if (is_cache_miss) {
user_misses_ += 1;
}
}
}
Cache::Priority PrioritizedCacheSimulator::ComputeBlockPriority(
const BlockCacheTraceRecord& access) const {
if (access.block_type == TraceType::kBlockTraceFilterBlock ||
access.block_type == TraceType::kBlockTraceIndexBlock ||
access.block_type == TraceType::kBlockTraceUncompressionDictBlock) {
return Cache::Priority::HIGH;
}
return Cache::Priority::LOW;
}
void PrioritizedCacheSimulator::AccessKVPair(
const Slice& key, uint64_t value_size, Cache::Priority priority,
const BlockCacheTraceRecord& access, bool no_insert, bool is_user_access,
bool* is_cache_miss, bool* admitted, bool update_metrics) {
assert(is_cache_miss);
assert(admitted);
*is_cache_miss = true;
*admitted = true;
if (ghost_cache_ && !no_insert) {
*admitted = ghost_cache_->Admit(key);
}
auto handle = sim_cache_->Lookup(key);
if (handle != nullptr) {
sim_cache_->Release(handle);
*is_cache_miss = false;
} else if (!no_insert && *admitted && value_size > 0) {
// TODO: Should we check for an error here?
auto s = sim_cache_->Insert(key, /*obj=*/nullptr, &kNoopCacheItemHelper,
value_size,
/*handle=*/nullptr, priority);
s.PermitUncheckedError();
}
if (update_metrics) {
miss_ratio_stats_.UpdateMetrics(access.access_timestamp, is_user_access,
*is_cache_miss);
}
}
void PrioritizedCacheSimulator::Access(const BlockCacheTraceRecord& access) {
bool is_cache_miss = true;
bool admitted = true;
AccessKVPair(access.block_key, access.block_size,
ComputeBlockPriority(access), access, access.no_insert,
BlockCacheTraceHelper::IsUserAccess(access.caller),
&is_cache_miss, &admitted, /*update_metrics=*/true);
}
void HybridRowBlockCacheSimulator::Access(const BlockCacheTraceRecord& access) {
// TODO (haoyu): We only support Get for now. We need to extend the tracing
// for MultiGet, i.e., non-data block accesses must log all keys in a
// MultiGet.
bool is_cache_miss = true;
bool admitted = false;
if (access.caller == TableReaderCaller::kUserGet &&
access.get_id != BlockCacheTraceHelper::kReservedGetId) {
// This is a Get request.
const std::string& row_key = BlockCacheTraceHelper::ComputeRowKey(access);
GetRequestStatus& status = getid_status_map_[access.get_id];
if (status.is_complete) {
// This Get request completes.
// Skip future accesses to its index/filter/data
// blocks. These block lookups are unnecessary if we observe a hit for the
// referenced key-value pair already. Thus, we treat these lookups as
// hits. This is also to ensure the total number of accesses are the same
// when comparing to other policies.
miss_ratio_stats_.UpdateMetrics(access.access_timestamp,
/*is_user_access=*/true,
/*is_cache_miss=*/false);
return;
}
if (status.row_key_status.find(row_key) == status.row_key_status.end()) {
// This is the first time that this key is accessed. Look up the key-value
// pair first. Do not update the miss/accesses metrics here since it will
// be updated later.
AccessKVPair(row_key, access.referenced_data_size, Cache::Priority::HIGH,
access,
/*no_insert=*/false,
/*is_user_access=*/true, &is_cache_miss, &admitted,
/*update_metrics=*/false);
InsertResult result = InsertResult::NO_INSERT;
if (admitted && access.referenced_data_size > 0) {
result = InsertResult::INSERTED;
} else if (admitted) {
result = InsertResult::ADMITTED;
}
status.row_key_status[row_key] = result;
}
if (!is_cache_miss) {
// A cache hit.
status.is_complete = true;
miss_ratio_stats_.UpdateMetrics(access.access_timestamp,
/*is_user_access=*/true,
/*is_cache_miss=*/false);
return;
}
// The row key-value pair observes a cache miss. We need to access its
// index/filter/data blocks.
InsertResult inserted = status.row_key_status[row_key];
AccessKVPair(
access.block_key, access.block_size, ComputeBlockPriority(access),
access,
/*no_insert=*/!insert_blocks_upon_row_kvpair_miss_ || access.no_insert,
/*is_user_access=*/true, &is_cache_miss, &admitted,
/*update_metrics=*/true);
if (access.referenced_data_size > 0 && inserted == InsertResult::ADMITTED) {
// TODO: Should we check for an error here?
auto s =
sim_cache_->Insert(row_key, /*obj=*/nullptr, &kNoopCacheItemHelper,
access.referenced_data_size,
/*handle=*/nullptr, Cache::Priority::HIGH);
s.PermitUncheckedError();
status.row_key_status[row_key] = InsertResult::INSERTED;
}
return;
}
AccessKVPair(access.block_key, access.block_size,
ComputeBlockPriority(access), access, access.no_insert,
BlockCacheTraceHelper::IsUserAccess(access.caller),
&is_cache_miss, &admitted, /*update_metrics=*/true);
}
BlockCacheTraceSimulator::BlockCacheTraceSimulator(
uint64_t warmup_seconds, uint32_t downsample_ratio,
const std::vector<CacheConfiguration>& cache_configurations)
: warmup_seconds_(warmup_seconds),
downsample_ratio_(downsample_ratio),
cache_configurations_(cache_configurations) {}
Status BlockCacheTraceSimulator::InitializeCaches() {
for (auto const& config : cache_configurations_) {
for (auto cache_capacity : config.cache_capacities) {
// Scale down the cache capacity since the trace contains accesses on
// 1/'downsample_ratio' blocks.
uint64_t simulate_cache_capacity = cache_capacity / downsample_ratio_;
std::shared_ptr<CacheSimulator> sim_cache;
std::unique_ptr<GhostCache> ghost_cache;
std::string cache_name = config.cache_name;
if (cache_name.find(kGhostCachePrefix) != std::string::npos) {
ghost_cache.reset(new GhostCache(
NewLRUCache(config.ghost_cache_capacity, /*num_shard_bits=*/1,
/*strict_capacity_limit=*/false,
/*high_pri_pool_ratio=*/0)));
cache_name = cache_name.substr(kGhostCachePrefix.size());
}
if (cache_name == "lru") {
sim_cache = std::make_shared<CacheSimulator>(
std::move(ghost_cache),
NewLRUCache(simulate_cache_capacity, config.num_shard_bits,
/*strict_capacity_limit=*/false,
/*high_pri_pool_ratio=*/0));
} else if (cache_name == "lru_priority") {
sim_cache = std::make_shared<PrioritizedCacheSimulator>(
std::move(ghost_cache),
NewLRUCache(simulate_cache_capacity, config.num_shard_bits,
/*strict_capacity_limit=*/false,
/*high_pri_pool_ratio=*/0.5));
} else if (cache_name == "lru_hybrid") {
sim_cache = std::make_shared<HybridRowBlockCacheSimulator>(
std::move(ghost_cache),
NewLRUCache(simulate_cache_capacity, config.num_shard_bits,
/*strict_capacity_limit=*/false,
/*high_pri_pool_ratio=*/0.5),
/*insert_blocks_upon_row_kvpair_miss=*/true);
} else if (cache_name == "lru_hybrid_no_insert_on_row_miss") {
sim_cache = std::make_shared<HybridRowBlockCacheSimulator>(
std::move(ghost_cache),
NewLRUCache(simulate_cache_capacity, config.num_shard_bits,
/*strict_capacity_limit=*/false,
/*high_pri_pool_ratio=*/0.5),
/*insert_blocks_upon_row_kvpair_miss=*/false);
} else {
// Not supported.
return Status::InvalidArgument("Unknown cache name " +
config.cache_name);
}
sim_caches_[config].push_back(sim_cache);
}
}
return Status::OK();
}
void BlockCacheTraceSimulator::Access(const BlockCacheTraceRecord& access) {
if (trace_start_time_ == 0) {
trace_start_time_ = access.access_timestamp;
}
// access.access_timestamp is in microseconds.
if (!warmup_complete_ &&
trace_start_time_ + warmup_seconds_ * kMicrosInSecond <=
access.access_timestamp) {
for (auto& config_caches : sim_caches_) {
for (auto& sim_cache : config_caches.second) {
sim_cache->reset_counter();
}
}
warmup_complete_ = true;
}
for (auto& config_caches : sim_caches_) {
for (auto& sim_cache : config_caches.second) {
sim_cache->Access(access);
}
}
}
} // namespace ROCKSDB_NAMESPACE