> ## 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.

# prefer_fetch_* MergeTree table settings

> ClickHouse MergeTree table settings in the prefer_fetch_* 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.merge\_tree\_settings](/docs/reference/system-tables/merge_tree_settings) and are autogenerated from ClickHouse source.

<h2 id="prefer_fetch_merged_part_size_threshold">
  prefer\_fetch\_merged\_part\_size\_threshold
</h2>

<SettingsInfoBlock type="UInt64" default_value="10737418240" />

If the sum of the size of parts exceeds this threshold and the time since a
replication log entry creation is greater than
`prefer_fetch_merged_part_time_threshold`, then prefer fetching merged part
from a replica instead of doing merge locally. This is to speed up very long
merges.

Possible values:

* Any positive integer.

<h2 id="prefer_fetch_merged_part_time_threshold">
  prefer\_fetch\_merged\_part\_time\_threshold
</h2>

<SettingsInfoBlock type="Seconds" default_value="3600" />

If the time passed since a replication log (ClickHouse Keeper or ZooKeeper)
entry creation exceeds this threshold, and the sum of the size of parts is
greater than `prefer_fetch_merged_part_size_threshold`, then prefer fetching
merged part from a replica instead of doing merge locally. This is to speed
up very long merges.

Possible values:

* Any positive integer.