> ## 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.
# allow_* session settings
> ClickHouse session settings in the allow_* generated group.
export const SettingsInfoBlock = ({type, default_value, changeable_without_restart}) => {
return
;
};
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).
allow\_aggregate\_partitions\_independently
Enable independent aggregation of partitions on separate threads when partition key suits group by key. Beneficial when number of partitions close to number of cores and partitions have roughly the same size. Heuristics in `ReadFromMergeTree` automatically disable the optimization for unfavorable layouts (too few partitions, too many partitions, or significantly skewed partition sizes); see `force_aggregate_partitions_independently` to bypass those checks.
allow\_archive\_path\_syntax
File/S3 engines/table function will parse paths with '::' as ` :: ` if the archive has correct extension.
If it's enabled, in hedged requests we can start new connection until receiving first data packet even if we have already made some progress
(but progress haven't updated for `receive_data_timeout` timeout), otherwise we disable changing replica after the first time we made progress.
allow\_create\_index\_without\_type
Allow CREATE INDEX query without TYPE. Query will be ignored. Made for SQL compatibility tests.
allow\_custom\_error\_code\_in\_throwif
Enable custom error code in function throwIf(). If true, thrown exceptions may have unexpected error codes.
allow\_ddl
If it is set to true, then a user is allowed to executed DDL queries.
allow\_distributed\_ddl
If it is set to true, then a user is allowed to executed distributed DDL queries.
allow\_drop\_detached
Allow ALTER TABLE ... DROP DETACHED PART\[ITION] ... queries
allow\_dynamic\_type\_in\_join\_keys
Allows using Dynamic type in JOIN keys. Added for compatibility. It's not recommended to use Dynamic type in JOIN keys because comparison with other types may lead to unexpected results.
allow\_execute\_multiif\_columnar
Allow execute multiIf function columnar
allow\_fuzz\_query\_functions
Enables the `fuzzQuery` function that applies random AST mutations to a query string.
allow\_general\_join\_planning
Allows a more general join planning algorithm that can handle more complex conditions, but only works with hash join. If hash join is not enabled, then the usual join planning algorithm is used regardless of the value of this setting.
allow\_get\_client\_http\_header
Allow to use the function `getClientHTTPHeader` which lets to obtain a value of the current HTTP request's header. It is not enabled by default for security reasons, because some headers, such as `Cookie`, could contain sensitive info. Note that the `X-ClickHouse-*`, `Authentication` and `Authorization` headers are always restricted and cannot be obtained with this function.
allow\_hyperscan
Allow functions that use Hyperscan library. Disable to avoid potentially long compilation times and excessive resource usage.
allow\_iceberg\_remove\_orphan\_files
Allow to use 'ALTER TABLE ... EXECUTE remove\_orphan\_files()' for iceberg tables.
allow\_insert\_into\_iceberg
**Aliases**: `allow_experimental_insert_into_iceberg`
Allow to execute `insert` queries into iceberg.
allow\_introspection\_functions
Enables or disables [introspection functions](/docs/reference/functions/regular-functions/introspection) for query profiling.
Possible values:
* 1 — Introspection functions enabled.
* 0 — Introspection functions disabled.
**See Also**
* [Sampling Query Profiler](/docs/concepts/features/performance/troubleshoot/sampling-query-profiler)
* System table [trace\_log](/docs/reference/system-tables/trace_log)
allow\_key\_condition\_coalesce\_rewrite
const` (and equivalently `ifNull`, or with the constant on the left) into a disjunction before index analysis, so per-column primary key and skip indexes on each `a_i` can be used. Partial-constant forms such as `coalesce(a, 42, b)` and `coalesce(a, b, 42)` are also handled."}]}]} />
Allow the MergeTree primary key and skip indexes to prune granules for `WHERE`/`PREWHERE` predicates that involve `coalesce` or `ifNull`. Without this setting, such predicates are opaque to index analysis and do not prune, so granules that cannot match are still read. This affects only which granules are read; query results are unchanged, because rows are still filtered by the original predicate.
Two predicate shapes are rewritten before index analysis:
* A comparison against a `coalesce`/`ifNull`, such as `coalesce(a, b) = 5`, becomes a disjunction so an index on each argument can prune: `a = 5 OR (a IS NULL AND b = 5)`, extended for more arguments.
* A `coalesce`/`ifNull` with a falsy (zero) constant default used directly as a condition, such as `ifNull(a = 5, 0)` or `coalesce(a = 5, 0)`, is unwrapped to its inner predicate `a = 5`. Such wrappers collapse the inner predicate's three-valued result into a definite boolean (mapping `NULL` to `false`).
allow\_limit\_by\_partitions\_independently
Enable independent `LIMIT BY` evaluation per partition on separate threads when the partition expression is a deterministic function of the `LIMIT BY` columns.
allow\_materialized\_view\_with\_bad\_select
Allow CREATE MATERIALIZED VIEW with SELECT query that references nonexistent tables or columns. It must still be syntactically valid. Doesn't apply to refreshable MVs. Doesn't apply if the MV schema needs to be inferred from the SELECT query (i.e. if the CREATE has no column list and no TO table). Can be used for creating MV before its source table.
allow\_minmax\_index\_for\_json
Allow creating minmax skip indexes on JSON (Object) columns. Disabled by default because the minmax
index serialization path cannot handle heterogeneous Field values that JSON columns may contain.
allow\_named\_collection\_override\_by\_default
Allow named collections' fields override by default.
allow\_non\_metadata\_alters
Allow to execute alters which affects not only tables metadata, but also data on disk
allow\_nonconst\_timezone\_arguments
Allow non-const timezone arguments in certain time-related functions like toTimeZone(), fromUnixTimestamp\*(), snowflakeIDToDateTime\*().
This setting exists only for compatibility reasons. In ClickHouse, the time zone is a property of the data type, respectively of the column.
Enabling this setting gives the wrong impression that different values within a column can have different timezones.
Therefore, please do not enable this setting.
allow\_nullable\_tuple\_in\_extracted\_subcolumns
Controls whether extracted subcolumns of type `Tuple(...)` can be typed as `Nullable(Tuple(...))`.
* `false`: Return `Tuple(...)` and use default tuple values for rows where the subcolumn is missing.
* `true`: Return `Nullable(Tuple(...))` and use `NULL` for rows where the subcolumn is missing.
This setting controls extracted subcolumn behavior only.
It does not control whether `Nullable(Tuple(...))` columns can be created in tables; that is controlled by `enable_nullable_tuple_type`.
ClickHouse uses the value for this setting loaded at server startup.
Changes made with `SET` or query-level `SETTINGS` do not change extracted subcolumn behavior.
To change extracted subcolumn behavior, update `allow_nullable_tuple_in_extracted_subcolumns` in startup profile configuration (for example, users.xml) and restart the server.
allow\_rank\_dense\_rank\_arguments
Allow passing arguments to the `RANK` and `DENSE_RANK` window functions for backward compatibility.
Per SQL standard, `RANK` and `DENSE_RANK` take zero arguments — they rank rows based on the
`OVER (ORDER BY ...)` window only. In ClickHouse versions before 26.5, queries such as
`RANK(x) OVER (...)` silently accepted and ignored the argument, which led to user confusion
(the visible argument suggested it influenced the ranking, but it did not).
When this setting is `false` (the default), `RANK` and `DENSE_RANK` reject any arguments and
throw `NUMBER_OF_ARGUMENTS_DOESNT_MATCH`. When set to `true`, the legacy lenient behavior is
restored — arguments are silently ignored, matching the pre-26.5 behavior.
allow\_reorder\_prewhere\_conditions
When moving conditions from WHERE to PREWHERE, allow reordering them to optimize filtering
allow\_replace\_partition\_from\_empty\_source
Allow `ALTER TABLE ... REPLACE PARTITION ... FROM ...` to silently drop the destination partition when the source has no parts in that partition.
By default this is disallowed: `REPLACE PARTITION` from a source that has no data in the requested partition raises an exception, because in this case the operation effectively becomes a silent `DROP PARTITION` on the destination (the destination's data is removed and nothing replaces it), a common cause of accidental data loss (see [#23727](https://github.com/ClickHouse/ClickHouse/issues/23727)).
Enable this setting to restore the previous behavior, for example when you intentionally use an empty source partition to clear data in the destination. For an unconditional drop, prefer `ALTER TABLE ... DROP PARTITION ...` instead.
allow\_settings\_after\_format\_in\_insert
Control whether `SETTINGS` after `FORMAT` in `INSERT` queries is allowed or not. It is not recommended to use this, since this may interpret part of `SETTINGS` as values.
Example:
```sql theme={null}
INSERT INTO FUNCTION null('foo String') SETTINGS max_threads=1 VALUES ('bar');
```
But the following query will work only with `allow_settings_after_format_in_insert`:
```sql theme={null}
SET allow_settings_after_format_in_insert=1;
INSERT INTO FUNCTION null('foo String') VALUES ('bar') SETTINGS max_threads=1;
```
Possible values:
* 0 — Disallow.
* 1 — Allow.
Use this setting only for backward compatibility if your use cases depend on old syntax.
allow\_simdjson
Allow using simdjson library in 'JSON\*' functions if AVX2 instructions are available. If disabled rapidjson will be used.
Allows to output columns with special serialization kinds like Sparse and Replicated without converting them to full column representation.
It helps to avoid unnecessary data copy during formatting.
allow\_unrestricted\_reads\_from\_keeper
Allow unrestricted (without condition on path) reads from system.zookeeper table, can be handy, but is not safe for zookeeper