rocksdb/db/write_controller.h

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
#pragma once
#include <stdint.h>
#include <memory>
namespace rocksdb {
class Env;
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)
: total_stopped_(0),
total_delayed_(0),
bytes_left_(0),
last_refill_time_(0) {
set_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();
// these two metods are querying the state of the WriteController
bool IsStopped() const;
bool NeedsDelay() const { return total_delayed_ > 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(Env* env, uint64_t num_bytes);
void set_delayed_write_rate(uint64_t delayed_write_rate) {
delayed_write_rate_ = delayed_write_rate;
if (delayed_write_rate_ == 0) {
// avoid divide 0
delayed_write_rate_ = 1U;
}
}
private:
friend class WriteControllerToken;
friend class StopWriteToken;
friend class DelayWriteToken;
int total_stopped_;
int total_delayed_;
uint64_t bytes_left_;
uint64_t last_refill_time_;
uint64_t delayed_write_rate_;
};
class WriteControllerToken {
public:
explicit WriteControllerToken(WriteController* controller)
: controller_(controller) {}
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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) {}
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virtual ~StopWriteToken();
};
class DelayWriteToken : public WriteControllerToken {
public:
explicit DelayWriteToken(WriteController* controller)
: WriteControllerToken(controller) {}
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virtual ~DelayWriteToken();
};
} // namespace rocksdb