> ## 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.

# page_cache_* session settings

> ClickHouse session settings in the page_cache_* 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="page_cache_block_size">
  page\_cache\_block\_size
</h2>

<SettingsInfoBlock type="UInt64" default_value="1048576" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "25.5"},{"label": "1048576"},{"label": "Made this setting adjustable on a per-query level."}]}]} />

Size of file chunks to store in the userspace page cache, in bytes. All reads that go through the cache will be rounded up to a multiple of this size.

This setting can be adjusted on a per-query level basis, but cache entries with different block sizes cannot be reused. Changing this setting effectively invalidates existing entries in the cache.

A higher value, like 1 MiB is good for high-throughput queries, and a lower value, like 64 KiB is good for low-latency point queries.

<h2 id="page_cache_inject_eviction">
  page\_cache\_inject\_eviction
</h2>

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

<VersionHistory rows={[{"id": "row-1","items": [{"label": "24.3"},{"label": "0"},{"label": "Added userspace page cache"}]}]} />

Userspace page cache will sometimes invalidate some pages at random. Intended for testing.

<h2 id="page_cache_lookahead_blocks">
  page\_cache\_lookahead\_blocks
</h2>

<SettingsInfoBlock type="UInt64" default_value="16" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "25.5"},{"label": "16"},{"label": "Made this setting adjustable on a per-query level."}]}]} />

On userspace page cache miss, read up to this many consecutive blocks at once from the underlying storage, if they're also not in the cache. Each block is page\_cache\_block\_size bytes.

A higher value is good for high-throughput queries, while low-latency point queries will work better without readahead.

<h2 id="page_cache_max_coalesced_bytes">
  page\_cache\_max\_coalesced\_bytes
</h2>

<SettingsInfoBlock type="UInt64" default_value="16777216" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.5"},{"label": "16777216"},{"label": "New setting to bound the size of a single coalesced read used to populate the userspace page cache on cache miss."}]}]} />

When `readBigAt` populates the userspace page cache, consecutive cache misses are coalesced into a single read from the underlying storage. This setting bounds the size of one coalesced read in bytes; longer miss runs are split into multiple reads. It limits transient memory usage of the temporary buffer under parallel cold reads.

A higher value reduces the number of HTTP requests for cold scans on object storage; a lower value reduces peak transient memory.