text: //  Copyright (c) 2014, 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.
  //
  // 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.
  
  #pragma once
  
  #include "rocksdb/env.h"
  
  namespace rocksdb {
  
  class RateLimiter {
   public:
    virtual ~RateLimiter() {}
  
    // This API allows user to dynamically change rate limiter's bytes per second.
    // REQUIRED: bytes_per_second > 0
    virtual void SetBytesPerSecond(int64_t bytes_per_second) = 0;
  
    // Request for token to write bytes. If this request can not be satisfied,
    // the call is blocked. Caller is responsible to make sure
    // bytes < GetSingleBurstBytes()
    virtual void Request(const int64_t bytes, const Env::IOPriority pri) = 0;
  
    // Max bytes can be granted in a single burst
    virtual int64_t GetSingleBurstBytes() const = 0;
  
    // Total bytes that go though rate limiter
    virtual int64_t GetTotalBytesThrough(
        const Env::IOPriority pri = Env::IO_TOTAL) const = 0;
  
    // Total # of requests that go though rate limiter
    virtual int64_t GetTotalRequests(
        const Env::IOPriority pri = Env::IO_TOTAL) const = 0;
  };
  
  // Create a RateLimiter object, which can be shared among RocksDB instances to
  // control write rate of flush and compaction.
  // @rate_bytes_per_sec: this is the only parameter you want to set most of the
  // time. It controls the total write rate of compaction and flush in bytes per
  // second. Currently, RocksDB does not enforce rate limit for anything other
  // than flush and compaction, e.g. write to WAL.
  // @refill_period_us: this controls how often tokens are refilled. For example,
  // when rate_bytes_per_sec is set to 10MB/s and refill_period_us is set to
  // 100ms, then 1MB is refilled every 100ms internally. Larger value can lead to
  // burstier writes while smaller value introduces more CPU overhead.
  // The default should work for most cases.
  // @fairness: RateLimiter accepts high-pri requests and low-pri requests.
  // A low-pri request is usually blocked in favor of hi-pri request. Currently,
  // RocksDB assigns low-pri to request from compaciton and high-pri to request
  // from flush. Low-pri requests can get blocked if flush requests come in
  // continuouly. This fairness parameter grants low-pri requests permission by
  // 1/fairness chance even though high-pri requests exist to avoid starvation.
  // You should be good by leaving it at default 10.
  extern RateLimiter* NewGenericRateLimiter(
      int64_t rate_bytes_per_sec,
      int64_t refill_period_us = 100 * 1000,
      int32_t fairness = 10);
  
  }  // namespace rocksdb
  