> ## 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.

# reader_executor_* session settings

> ClickHouse session settings in the reader_executor_* 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>;
};

export const ExperimentalBadge = () => {
  return <div className="experimentalBadge">
            <div className="experimentalIcon">
            <svg width="16" height="16" viewBox="0 0 16 16" fill="none" xmlns="http://www.w3.org/2000/svg">
                <path strokeWidth="1.25" d="M5.5 2H10.5" stroke="currentColor" strokeLinecap="round" strokeLinejoin="round" />
                <path strokeWidth="1.25" d="M9.50015 2V6.19625L13.4283 12.7425C13.4738 12.8183 13.4985 12.9049 13.4996 12.9934C13.5008 13.0818 13.4785 13.169 13.435 13.246C13.3914 13.323 13.3283 13.3871 13.2519 13.4317C13.1755 13.4764 13.0886 13.4999 13.0002 13.5H3.00015C2.91164 13.5 2.8247 13.4766 2.74822 13.432C2.67174 13.3874 2.60847 13.3233 2.56487 13.2463C2.52126 13.1693 2.49889 13.082 2.50004 12.9935C2.50119 12.905 2.52582 12.8184 2.5714 12.7425L6.50015 6.19625V2" stroke="currentColor" strokeLinecap="round" strokeLinejoin="round" />
                <path strokeWidth="1.25" d="M4.47656 9.56754C5.30344 9.41254 6.47656 9.47942 7.99969 10.25C10.0153 11.2707 11.4216 11.0569 12.2184 10.7282" stroke="currentColor" strokeLinecap="round" strokeLinejoin="round" />
            </svg>
        </div>
            Experimental feature. <u><a href="/docs/docs/beta-and-experimental-features#experimental-features">Learn more.</a></u>
        </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="reader_executor_max_tail_for_drain">
  reader\_executor\_max\_tail\_for\_drain
</h2>

<ExperimentalBadge />

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

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.7"},{"label": "1048576"},{"label": "New experimental ReaderExecutor setting: drain bound for completing a dropped long connection."}]}]} />

Drain bound for the experimental `ReaderExecutor`: a long source connection dropped within this many bytes of its right bound is read out to the bound first, so it completes and returns to the connection pool reusable instead of counting as an incomplete connection.

<h2 id="reader_executor_min_bytes_for_seek">
  reader\_executor\_min\_bytes\_for\_seek
</h2>

<ExperimentalBadge />

<SettingsInfoBlock type="UInt64" default_value="2097152" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.7"},{"label": "2097152"},{"label": "New experimental ReaderExecutor setting: forward-gap bound for bridging on a held source connection."}]}]} />

Forward-gap bound for the experimental `ReaderExecutor`: a gap up to this is skipped on the open source connection (bridged / read through) instead of issuing a separate source read or reopening. Set near the bandwidth/request cost breakeven so bridging stays cost-positive.

<h2 id="reader_executor_use_long_connections">
  reader\_executor\_use\_long\_connections
</h2>

<ExperimentalBadge />

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

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.7"},{"label": "0"},{"label": "New experimental ReaderExecutor setting (off by default): reuse a held source connection across sequential windows."}]}]} />

Reuse a bounded long source connection across windows in the experimental `ReaderExecutor`. A long connection is one whose range exceeds the current read window; when disabled, the executor takes no connection-pool budget and every window opens a short-lived one-shot connection (the stateless path).