> ## 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.

# preferred_* session settings

> ClickHouse session settings in the preferred_* 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="preferred_block_size_bytes">
  preferred\_block\_size\_bytes
</h2>

<SettingsInfoBlock type="UInt64" default_value="1000000" />

This setting adjusts the data block size for query processing and represents additional fine-tuning to the more rough 'max\_block\_size' setting. If the columns are large and with 'max\_block\_size' rows the block size is likely to be larger than the specified amount of bytes, its size will be lowered for better CPU cache locality.

<h2 id="preferred_max_column_in_block_size_bytes">
  preferred\_max\_column\_in\_block\_size\_bytes
</h2>

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

Limit on max column size in block while reading. Helps to decrease cache misses count. Should be close to L2 cache size.

<h2 id="preferred_optimize_projection_name">
  preferred\_optimize\_projection\_name
</h2>

If it is set to a non-empty string, ClickHouse will try to apply specified projection in query.

Possible values:

* string: name of preferred projectio