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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 "db/write_controller.h"
#include <atomic>
#include <cassert>
#include <ratio>
#include "rocksdb/env.h"
namespace rocksdb {
std::unique_ptr<WriteControllerToken> WriteController::GetStopToken() {
++total_stopped_;
return std::unique_ptr<WriteControllerToken>(new StopWriteToken(this));
}
std::unique_ptr<WriteControllerToken> WriteController::GetDelayToken(
uint64_t write_rate) {
total_delayed_++;
// Reset counters.
last_refill_time_ = 0;
bytes_left_ = 0;
set_delayed_write_rate(write_rate);
return std::unique_ptr<WriteControllerToken>(new DelayWriteToken(this));
}
std::unique_ptr<WriteControllerToken>
WriteController::GetCompactionPressureToken() {
++total_compaction_pressure_;
return std::unique_ptr<WriteControllerToken>(
new CompactionPressureToken(this));
}
bool WriteController::IsStopped() const {
return total_stopped_.load(std::memory_order_relaxed) > 0;
}
// This is inside DB mutex, so we can't sleep and need to minimize
// frequency to get time.
// If it turns out to be a performance issue, we can redesign the thread
// synchronization model here.
// The function trust caller will sleep micros returned.
uint64_t WriteController::GetDelay(Env* env, uint64_t num_bytes) {
if (total_stopped_.load(std::memory_order_relaxed) > 0) {
return 0;
}
if (total_delayed_.load(std::memory_order_relaxed) == 0) {
return 0;
}
const uint64_t kMicrosPerSecond = 1000000;
const uint64_t kRefillInterval = 1024U;
if (bytes_left_ >= num_bytes) {
bytes_left_ -= num_bytes;
return 0;
}
// The frequency to get time inside DB mutex is less than one per refill
// interval.
auto time_now = NowMicrosMonotonic(env);
uint64_t sleep_debt = 0;
uint64_t time_since_last_refill = 0;
if (last_refill_time_ != 0) {
if (last_refill_time_ > time_now) {
sleep_debt = last_refill_time_ - time_now;
} else {
time_since_last_refill = time_now - last_refill_time_;
bytes_left_ +=
static_cast<uint64_t>(static_cast<double>(time_since_last_refill) /
kMicrosPerSecond * delayed_write_rate_);
if (time_since_last_refill >= kRefillInterval &&
bytes_left_ > num_bytes) {
// If refill interval already passed and we have enough bytes
// return without extra sleeping.
last_refill_time_ = time_now;
bytes_left_ -= num_bytes;
return 0;
}
}
}
uint64_t single_refill_amount =
delayed_write_rate_ * kRefillInterval / kMicrosPerSecond;
if (bytes_left_ + single_refill_amount >= num_bytes) {
// Wait until a refill interval
// Never trigger expire for less than one refill interval to avoid to get
// time.
bytes_left_ = bytes_left_ + single_refill_amount - num_bytes;
last_refill_time_ = time_now + kRefillInterval;
return kRefillInterval + sleep_debt;
}
// Need to refill more than one interval. Need to sleep longer. Check
// whether expiration will hit
// Sleep just until `num_bytes` is allowed.
uint64_t sleep_amount =
static_cast<uint64_t>(num_bytes /
static_cast<long double>(delayed_write_rate_) *
kMicrosPerSecond) +
sleep_debt;
last_refill_time_ = time_now + sleep_amount;
return sleep_amount;
}
uint64_t WriteController::NowMicrosMonotonic(Env* env) {
return env->NowNanos() / std::milli::den;
}
StopWriteToken::~StopWriteToken() {
assert(controller_->total_stopped_ >= 1);
--controller_->total_stopped_;
}
DelayWriteToken::~DelayWriteToken() {
controller_->total_delayed_--;
assert(controller_->total_delayed_.load() >= 0);
}
CompactionPressureToken::~CompactionPressureToken() {
controller_->total_compaction_pressure_--;
assert(controller_->total_compaction_pressure_ >= 0);
}
} // namespace rocksdb
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