> ## 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.

# parallel_* session settings

> ClickHouse session settings in the parallel_* 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>;
};

export const BetaBadge = ({link, galaxyTrack, galaxyEvent}) => {
  if (link) {
    return <a href={link} target="_blank" rel="noopener noreferrer" className="betaBadge" onClick={galaxyTrack && galaxyEvent ? galaxyOnClick(galaxyEvent) : undefined}>
                <Icon />
                <span>Beta</span>
            </a>;
  }
  return <div className="betaBadge">
            <Icon />
            <span>
                Beta feature. 
                <u>
                    <a href="/docs/docs/beta-and-experimental-features#beta-features">
                        Learn more.
                    </a>
                </u>
            </span>
        </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="parallel_distributed_insert_select">
  parallel\_distributed\_insert\_select
</h2>

<SettingsInfoBlock type="UInt64" default_value="2" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "25.7"},{"label": "2"},{"label": "Enable parallel distributed insert select by default"}]}]} />

Enables parallel distributed `INSERT ... SELECT` query.

If we execute `INSERT INTO distributed_table_a SELECT ... FROM distributed_table_b` queries and both tables use the same cluster, and both tables are either [replicated](/docs/reference/engines/table-engines/mergetree-family/replication) or non-replicated, then this query is processed locally on every shard.

Possible values:

* `0` — Disabled.
* `1` — `SELECT` will be executed on each shard from the underlying table of the distributed engine.
* `2` — `SELECT` and `INSERT` will be executed on each shard from/to the underlying table of the distributed engine.

Since v25.4, `INSERT ... SELECT` from a `ReplicatedMergeTree` or `SharedMergeTree` source can also be parallelized across replicas. To enable it:

* `parallel_distributed_insert_select = 2`
* `enable_parallel_replicas = 1`

<h2 id="parallel_hash_join_threshold">
  parallel\_hash\_join\_threshold
</h2>

<SettingsInfoBlock type="UInt64" default_value="100000" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "25.5"},{"label": "100000"},{"label": "New setting"}]}, {"id": "row-2","items": [{"label": "25.4"},{"label": "0"},{"label": "New setting"}]}, {"id": "row-3","items": [{"label": "25.3"},{"label": "0"},{"label": "New setting"}]}]} />

When hash-based join algorithm is applied, this threshold helps to decide between using `hash` and `parallel_hash` (only if estimation of the right table size is available).
The former is used when we know that the right table size is below the threshold.

<h2 id="parallel_non_joined_rows_processing">
  parallel\_non\_joined\_rows\_processing
</h2>

<SettingsInfoBlock type="Bool" default_value="1" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.2"},{"label": "1"},{"label": "New setting to enable parallel processing of non-joined rows in RIGHT\/FULL parallel_hash joins."}]}]} />

Allow multiple threads to process non-joined rows from the right table in parallel during RIGHT and FULL JOINs.
This can speed up the non-joined phase when using the `parallel_hash` join algorithm with large tables.
When disabled, non-joined rows are processed by a single thread.

<h2 id="parallel_replica_offset">
  parallel\_replica\_offset
</h2>

<BetaBadge />

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

This is internal setting that should not be used directly and represents an implementation detail of the 'parallel replicas' mode. This setting will be automatically set up by the initiator server for distributed queries to the index of the replica participating in query processing among parallel replicas.

<h2 id="parallel_view_processing">
  parallel\_view\_processing
</h2>

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

Enables pushing to attached views concurrently instead of sequentially.