> ## 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.

# optimize_use_* session settings

> ClickHouse session settings in the optimize_use_* 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="optimize_use_implicit_projections">
  optimize\_use\_implicit\_projections
</h2>

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

Automatically choose implicit projections to perform SELECT query

<h2 id="optimize_use_projection_filtering">
  optimize\_use\_projection\_filtering
</h2>

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

<VersionHistory rows={[{"id": "row-1","items": [{"label": "25.6"},{"label": "1"},{"label": "New setting"}]}]} />

Enables using projections to filter part ranges even when projections are not selected to perform SELECT query.

<h2 id="optimize_use_projections">
  optimize\_use\_projections
</h2>

**Aliases**: `allow_experimental_projection_optimization`

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

Enables or disables [projection](/docs/reference/engines/table-engines/mergetree-family/mergetree#projections) optimization when processing `SELECT` queries.

Possible values:

* 0 — Projection optimization disabled.
* 1 — Projection optimization enabled.