> ## 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.

# use_top_k_dynamic_filtering_* session settings

> ClickHouse session settings in the use_top_k_dynamic_filtering_* 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="use_top_k_dynamic_filtering">
  use\_top\_k\_dynamic\_filtering
</h2>

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

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.5"},{"label": "1"},{"label": "Enable dynamic filtering optimization for TopK queries by default"}]}, {"id": "row-2","items": [{"label": "25.12"},{"label": "0"},{"label": "New setting."}]}]} />

Enable dynamic filtering optimization when executing a `ORDER BY <column> LIMIT n` query.

When enabled, the query executor will try to skip granules and rows that will not be part of the final `top N` rows in the resultset. This optimization is dynamic in nature and latency improvements depends on data distribution and presence of other predicates in the query.

Possible values:

* 0 — Disabled.
* 1 — Enabled.

<h2 id="use_top_k_dynamic_filtering_for_variable_length_types">
  use\_top\_k\_dynamic\_filtering\_for\_variable\_length\_types
</h2>

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

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.5"},{"label": "0"},{"label": "Disable `use_top_k_dynamic_filtering` for variable-length sort columns (e.g. `String`) by default; the previous behavior had the optimization apply unconditionally and is preserved under `compatibility`."}]}]} />

Allow `use_top_k_dynamic_filtering` to apply when the sort column has a variable-length data type (e.g. `String`, `Array`, `Map`, `Tuple` containing variable-length elements).

For such types, the per-row threshold comparison performed by the dynamic filter can outweigh its savings when the column's lexicographic minimum dominates (e.g. mostly empty strings) and few granules can be skipped. In that case the dynamic filter degrades query latency rather than improving it.

When this setting is `0`, dynamic filtering is restricted to columns whose values have a fixed maximum size in memory (numbers, `Date`, `DateTime`, `FixedString`, `Enum`, `Nullable` of such types, `Tuple` of such types). When set to `1`, dynamic filtering applies to variable-length types as well.

Possible values:

* 0 — Disabled.
* 1 — Enabled.