> ## 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.

# external_storage_* session settings

> ClickHouse session settings in the external_storage_* generated group.

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
  }}>Type</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{type}</div>
      <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>Default</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{default_value}</div>
      {changeable_without_restart && <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>
          Changeable without restart
        </div>}
      {changeable_without_restart && <div style={{
    overflowWrap: "anywhere"
  }}>
          {changeable_without_restart}
        </div>}
    </div>;
};

These settings are available in [system.settings](/docs/reference/system-tables/settings) and are autogenerated from [source](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.cpp).

<h2 id="external_storage_connect_timeout_sec">
  external\_storage\_connect\_timeout\_sec
</h2>

<SettingsInfoBlock type="UInt64" default_value="10" />

Connect timeout in seconds. Now supported only for MySQL

<h2 id="external_storage_max_read_bytes">
  external\_storage\_max\_read\_bytes
</h2>

<SettingsInfoBlock type="UInt64" default_value="0" />

Limit maximum number of bytes when table with external engine should flush history data. Now supported only for MySQL table engine, database engine, and dictionary. If equal to 0, this setting is disabled

<h2 id="external_storage_max_read_rows">
  external\_storage\_max\_read\_rows
</h2>

<SettingsInfoBlock type="UInt64" default_value="0" />

Limit maximum number of rows when table with external engine should flush history data. Now supported only for MySQL table engine, database engine, and dictionary. If equal to 0, this setting is disabled

<h2 id="external_storage_rw_timeout_sec">
  external\_storage\_rw\_timeout\_sec
</h2>

<SettingsInfoBlock type="UInt64" default_value="300" />

Read/write timeout in seconds. Now supported only for MySQL