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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).
#pragma once
#include <stdint.h>
#include <atomic>
#include <memory>
#include "rocksdb/rate_limiter.h"
namespace ROCKSDB_NAMESPACE {
class SystemClock;
class WriteControllerToken;
// WriteController is controlling write stalls in our write code-path. Write
// stalls happen when compaction can't keep up with write rate.
// All of the methods here (including WriteControllerToken's destructors) need
// to be called while holding DB mutex
class WriteController {
public:
explicit WriteController(uint64_t _delayed_write_rate = 1024u * 1024u * 32u,
int64_t low_pri_rate_bytes_per_sec = 1024 * 1024)
: total_stopped_(0),
total_delayed_(0),
total_compaction_pressure_(0),
credit_in_bytes_(0),
next_refill_time_(0),
low_pri_rate_limiter_(
NewGenericRateLimiter(low_pri_rate_bytes_per_sec)) {
set_max_delayed_write_rate(_delayed_write_rate);
}
~WriteController() = default;
// When an actor (column family) requests a stop token, all writes will be
// stopped until the stop token is released (deleted)
std::unique_ptr<WriteControllerToken> GetStopToken();
// When an actor (column family) requests a delay token, total delay for all
// writes to the DB will be controlled under the delayed write rate. Every
// write needs to call GetDelay() with number of bytes writing to the DB,
// which returns number of microseconds to sleep.
std::unique_ptr<WriteControllerToken> GetDelayToken(
uint64_t delayed_write_rate);
// When an actor (column family) requests a moderate token, compaction
// threads will be increased
std::unique_ptr<WriteControllerToken> GetCompactionPressureToken();
// these three metods are querying the state of the WriteController
bool IsStopped() const;
bool NeedsDelay() const { return total_delayed_.load() > 0; }
bool NeedSpeedupCompaction() const {
return IsStopped() || NeedsDelay() || total_compaction_pressure_.load() > 0;
}
// return how many microseconds the caller needs to sleep after the call
// num_bytes: how many number of bytes to put into the DB.
// Prerequisite: DB mutex held.
uint64_t GetDelay(SystemClock* clock, uint64_t num_bytes);
void set_delayed_write_rate(uint64_t write_rate) {
// avoid divide 0
if (write_rate == 0) {
write_rate = 1u;
} else if (write_rate > max_delayed_write_rate()) {
write_rate = max_delayed_write_rate();
}
delayed_write_rate_ = write_rate;
}
void set_max_delayed_write_rate(uint64_t write_rate) {
// avoid divide 0
if (write_rate == 0) {
write_rate = 1u;
}
max_delayed_write_rate_ = write_rate;
// update delayed_write_rate_ as well
delayed_write_rate_ = write_rate;
}
uint64_t delayed_write_rate() const { return delayed_write_rate_; }
uint64_t max_delayed_write_rate() const { return max_delayed_write_rate_; }
RateLimiter* low_pri_rate_limiter() { return low_pri_rate_limiter_.get(); }
private:
uint64_t NowMicrosMonotonic(SystemClock* clock);
friend class WriteControllerToken;
friend class StopWriteToken;
friend class DelayWriteToken;
friend class CompactionPressureToken;
std::atomic<int> total_stopped_;
std::atomic<int> total_delayed_;
std::atomic<int> total_compaction_pressure_;
// Number of bytes allowed to write without delay
uint64_t credit_in_bytes_;
// Next time that we can add more credit of bytes
uint64_t next_refill_time_;
// Write rate set when initialization or by `DBImpl::SetDBOptions`
uint64_t max_delayed_write_rate_;
// Current write rate (bytes / second)
uint64_t delayed_write_rate_;
std::unique_ptr<RateLimiter> low_pri_rate_limiter_;
};
class WriteControllerToken {
public:
explicit WriteControllerToken(WriteController* controller)
: controller_(controller) {}
virtual ~WriteControllerToken() {}
protected:
WriteController* controller_;
private:
// no copying allowed
WriteControllerToken(const WriteControllerToken&) = delete;
void operator=(const WriteControllerToken&) = delete;
};
class StopWriteToken : public WriteControllerToken {
public:
explicit StopWriteToken(WriteController* controller)
: WriteControllerToken(controller) {}
virtual ~StopWriteToken();
};
class DelayWriteToken : public WriteControllerToken {
public:
explicit DelayWriteToken(WriteController* controller)
: WriteControllerToken(controller) {}
virtual ~DelayWriteToken();
};
class CompactionPressureToken : public WriteControllerToken {
public:
explicit CompactionPressureToken(WriteController* controller)
: WriteControllerToken(controller) {}
virtual ~CompactionPressureToken();
};
} // namespace ROCKSDB_NAMESPACE
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