> ## Documentation Index
> Fetch the complete documentation index at: https://clickhouse.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# read_backoff_* 会话设置

> ClickHouse 中 read_backoff_* 自动生成分组下的会话设置。

export const SettingsInfoBlock = ({type, default_value, changeable_without_restart}) => {
  return <div className="not-prose" style={{
    display: "flex",
    flexWrap: "wrap",
    alignItems: "baseline",
    columnGap: "0.5rem",
    rowGap: "0.125rem",
    margin: "0.375rem 0",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <div style={{
    fontWeight: 600,
    opacity: 0.72
  }}>类型</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{type}</div>
      <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>默认值</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{default_value}</div>
      {changeable_without_restart && <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>
          无需重启即可更改
        </div>}
      {changeable_without_restart && <div style={{
    overflowWrap: "anywhere"
  }}>
          {changeable_without_restart}
        </div>}
    </div>;
};

这些设置可在 [system.settings](/docs/zh/reference/system-tables/settings) 中查看，并由 [源代码](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.cpp) 自动生成。

<div id="read_backoff_max_throughput">
  ## read\_backoff\_max\_throughput
</div>

<SettingsInfoBlock type="UInt64" default_value="1048576" />

用于在读取速度较慢时减少线程数量的设置。当读取带宽低于该每秒字节数阈值时，开始计数事件。

<div id="read_backoff_min_concurrency">
  ## read\_backoff\_min\_concurrency
</div>

<SettingsInfoBlock type="UInt64" default_value="1" />

在读取速度较慢时，尝试保持最小线程数的设置。

<div id="read_backoff_min_events">
  ## read\_backoff\_min\_events
</div>

<SettingsInfoBlock type="UInt64" default_value="2" />

用于在磁盘读取速度较慢时减少线程数的设置。达到该事件次数后，将减少线程数。

<div id="read_backoff_min_interval_between_events_ms">
  ## read\_backoff\_min\_interval\_between\_events\_ms
</div>

<SettingsInfoBlock type="毫秒" default_value="1000" />

在读取速度较慢时，用于减少线程数量的设置。如果距离上一次事件发生的时间少于设定的时间间隔，则忽略该事件。

<div id="read_backoff_min_latency_ms">
  ## read\_backoff\_min\_latency\_ms
</div>

<SettingsInfoBlock type="毫秒" default_value="1000" />

用于在读取速度较慢时减少线程数量的设置。只考虑耗时至少达到该时长的读取操作。