> ## 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.

# local_filesystem_* session settings

> ClickHouse session settings in the local_filesystem_* 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="local_filesystem_read_method">
  local\_filesystem\_read\_method
</h2>

<SettingsInfoBlock type="String" default_value="pread_threadpool" />

Method of reading data from local filesystem, one of: read, pread, mmap, io\_uring, pread\_threadpool.

The 'io\_uring' method is experimental and does not work for Log, TinyLog, StripeLog, File, Set and Join, and other tables with append-able files in presence of concurrent reads and writes.
If you read various articles about 'io\_uring' on the Internet, don't be blinded by them. It is not a better method of reading files, unless the case of a large amount of small IO requests, which is not the case in ClickHouse. There are no reasons to enable 'io\_uring'.

<h2 id="local_filesystem_read_prefetch">
  local\_filesystem\_read\_prefetch
</h2>

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

Should use prefetching when reading data from local filesystem.