> ## 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.

# max_partitions_* session settings

> ClickHouse session settings in the max_partitions_* 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="max_partitions_per_insert_block">
  max\_partitions\_per\_insert\_block
</h2>

<SettingsInfoBlock type="UInt64" default_value="100" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "19.5"},{"label": "100"},{"label": "Add a limit for the number of partitions in one block"}]}]} />

Limits the maximum number of partitions in a single inserted block
and an exception is thrown if the block contains too many partitions.

* Positive integer.
* `0` — Unlimited number of partitions.

**Details**

When inserting data, ClickHouse calculates the number of partitions in the
inserted block. If the number of partitions is more than
`max_partitions_per_insert_block`, ClickHouse either logs a warning or throws an
exception based on `throw_on_max_partitions_per_insert_block`. Exceptions have
the following text:

> "Too many partitions for a single INSERT block (`partitions_count` partitions, limit is " + toString(max\_partitions) + ").
> The limit is controlled by the 'max\_partitions\_per\_insert\_block' setting.
> A large number of partitions is a common misconception. It will lead to severe
> negative performance impact, including slow server startup, slow INSERT queries
> and slow SELECT queries. Recommended total number of partitions for a table is
> under 1000..10000. Please note, that partitioning is not intended to speed up
> SELECT queries (ORDER BY key is sufficient to make range queries fast).
> Partitions are intended for data manipulation (DROP PARTITION, etc)."

<Note>
  This setting is a safety threshold because using a large number of partitions is a common misconception.
</Note>

<h2 id="max_partitions_to_read">
  max\_partitions\_to\_read
</h2>

<SettingsInfoBlock type="Int64" default_value="-1" />

Limits the maximum number of partitions that can be accessed in a single query.

The setting value specified when the table is created can be overridden via query-level setting.

Possible values:

* Positive integer
* `-1` - unlimited (default)

<Note>
  You can also specify the MergeTree setting [`max_partitions_to_read`](/docs/reference/settings/session-settings/max-partitions#max_partitions_to_read) in tables' setting.
</Note>