> ## 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.
# enable_* session settings
> ClickHouse session settings in the enable_* 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).
enable\_adaptive\_memory\_spill\_scheduler
Trigger processor to spill data into external storage adpatively. grace join is supported at present.
enable\_add\_distinct\_to\_in\_subqueries
Enable `DISTINCT` in `IN` subqueries. This is a trade-off setting: enabling it can greatly reduce the size of temporary tables transferred for distributed IN subqueries and significantly speed up data transfer between shards, by ensuring only unique values are sent.
However, enabling this setting adds extra merging effort on each node, as deduplication (DISTINCT) must be performed. Use this setting when network transfer is a bottleneck and the additional merging cost is acceptable.
If set, ClickHouse will automatically enable this optimization when the partition key expression is deterministic and all columns used in the partition key expression are included in the primary key.
This automatic derivation ensures that rows with the same primary key values will always belong to the same partition, making it safe to avoid cross-partition merges.
enable\_early\_constant\_folding
Enable query optimization where we analyze function and subqueries results and rewrite query if there are constants there
Enables or disables returning results of type `Date32` with extended range (compared to type `Date`)
or `DateTime64` with extended range (compared to type `DateTime`).
Possible values:
* `0` — Functions return `Date` or `DateTime` for all types of arguments.
* `1` — Functions return `Date32` or `DateTime64` for `Date32` or `DateTime64` arguments and `Date` or `DateTime` otherwise.
The table below shows the behavior of this setting for various date-time functions.
| Function | `enable_extended_results_for_datetime_functions = 0` | `enable_extended_results_for_datetime_functions = 1` |
| ------------------------- | -------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------ |
| `toStartOfYear` | Returns `Date` or `DateTime` | Returns `Date`/`DateTime` for `Date`/`DateTime` input Returns `Date32`/`DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfISOYear` | Returns `Date` or `DateTime` | Returns `Date`/`DateTime` for `Date`/`DateTime` input Returns `Date32`/`DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfQuarter` | Returns `Date` or `DateTime` | Returns `Date`/`DateTime` for `Date`/`DateTime` input Returns `Date32`/`DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfMonth` | Returns `Date` or `DateTime` | Returns `Date`/`DateTime` for `Date`/`DateTime` input Returns `Date32`/`DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfWeek` | Returns `Date` or `DateTime` | Returns `Date`/`DateTime` for `Date`/`DateTime` input Returns `Date32`/`DateTime64` for `Date32`/`DateTime64` input |
| `toLastDayOfWeek` | Returns `Date` or `DateTime` | Returns `Date`/`DateTime` for `Date`/`DateTime` input Returns `Date32`/`DateTime64` for `Date32`/`DateTime64` input |
| `toLastDayOfMonth` | Returns `Date` or `DateTime` | Returns `Date`/`DateTime` for `Date`/`DateTime` input Returns `Date32`/`DateTime64` for `Date32`/`DateTime64` input |
| `toMonday` | Returns `Date` or `DateTime` | Returns `Date`/`DateTime` for `Date`/`DateTime` input Returns `Date32`/`DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfDay` | Returns `DateTime` *Note: Wrong results for values outside 1970-2149 range* | Returns `DateTime` for `Date`/`DateTime` input Returns `DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfHour` | Returns `DateTime` *Note: Wrong results for values outside 1970-2149 range* | Returns `DateTime` for `Date`/`DateTime` input Returns `DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfFifteenMinutes` | Returns `DateTime` *Note: Wrong results for values outside 1970-2149 range* | Returns `DateTime` for `Date`/`DateTime` input Returns `DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfTenMinutes` | Returns `DateTime` *Note: Wrong results for values outside 1970-2149 range* | Returns `DateTime` for `Date`/`DateTime` input Returns `DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfFiveMinutes` | Returns `DateTime` *Note: Wrong results for values outside 1970-2149 range* | Returns `DateTime` for `Date`/`DateTime` input Returns `DateTime64` for `Date32`/`DateTime64` input |
| `toStartOfMinute` | Returns `DateTime` *Note: Wrong results for values outside 1970-2149 range* | Returns `DateTime` for `Date`/`DateTime` input Returns `DateTime64` for `Date32`/`DateTime64` input |
| `timeSlot` | Returns `DateTime` *Note: Wrong results for values outside 1970-2149 range* | Returns `DateTime` for `Date`/`DateTime` input Returns `DateTime64` for `Date32`/`DateTime64` input |
enable\_full\_text\_index
**Aliases**: `allow_experimental_full_text_index`
If set to true, allow using the text index.
enable\_global\_with\_statement
Propagate WITH statements to UNION queries and all subqueries
enable\_hdfs\_pread
Enable or disables pread for HDFS files. By default, `hdfsPread` is used. If disabled, `hdfsRead` and `hdfsSeek` will be used to read hdfs files.
enable\_http\_compression
Enables or disables data compression in the response to an HTTP request.
For more information, read the [HTTP interface description](/docs/concepts/features/interfaces/http).
Possible values:
* 0 — Disabled.
* 1 — Enabled.
enable\_identifier\_resolve\_cache
Enable the identifier resolution cache in the query analyzer. The cache shares resolved alias nodes to prevent AST explosion when the same alias is referenced multiple times. Set to false to disable caching if incorrect results are suspected.
enable\_job\_stack\_trace
Output stack trace of a job creator when job results in exception. Disabled by default to avoid performance overhead.
enable\_lazy\_columns\_replication
Enables lazy columns replication in JOIN and ARRAY JOIN, it allows to avoid unnecessary copy of the same rows multiple times in memory.
enable\_materialized\_cte
Enable materialized common table expressions, it will be preferred over enable\_global\_with\_statement
Enable memory bound merging strategy for aggregation.
enable\_multiple\_prewhere\_read\_steps
Move more conditions from WHERE to PREWHERE and do reads from disk and filtering in multiple steps if there are multiple conditions combined with AND
enable\_named\_columns\_in\_function\_tuple
Generate named tuples in function tuple() when all names are unique and can be treated as unquoted identifiers.
enable\_order\_by\_all
Enables or disables sorting with `ORDER BY ALL` syntax, see [ORDER BY](/docs/reference/statements/select/order-by).
Possible values:
* 0 — Disable ORDER BY ALL.
* 1 — Enable ORDER BY ALL.
**Example**
Query:
```sql theme={null}
CREATE TABLE TAB(C1 Int, C2 Int, ALL Int) ENGINE=Memory();
INSERT INTO TAB VALUES (10, 20, 30), (20, 20, 10), (30, 10, 20);
SELECT * FROM TAB ORDER BY ALL; -- returns an error that ALL is ambiguous
SELECT * FROM TAB ORDER BY ALL SETTINGS enable_order_by_all = 0;
```
Result:
```text theme={null}
┌─C1─┬─C2─┬─ALL─┐
│ 20 │ 20 │ 10 │
│ 30 │ 10 │ 20 │
│ 10 │ 20 │ 30 │
└────┴────┴─────┘
```
enable\_parallel\_blocks\_marshalling
Affects only distributed queries. If enabled, blocks will be (de)serialized and (de)compressed on pipeline threads (i.e. with higher parallelism that what we have by default) before/after sending to the initiator.
enable\_parsing\_to\_custom\_serialization
If true then data can be parsed directly to columns with custom serialization (e.g. Sparse) according to hints for serialization got from the table.
Allow memory-efficient aggregation (see `distributed_aggregation_memory_efficient`) to produce buckets out of order.
It may improve performance when aggregation bucket sizes are skewed by letting a replica to send buckets with higher id-s to the initiator while it is still processing some heavy buckets with lower id-s.
The downside is potentially higher memory usage.
enable\_reads\_from\_query\_cache
If turned on, results of `SELECT` queries are retrieved from the [query cache](/docs/concepts/features/performance/caches/query-cache).
Possible values:
* 0 - Disabled
* 1 - Enabled
enable\_s3\_requests\_logging
Enable very explicit logging of S3 requests. Makes sense for debug only.
enable\_scalar\_subquery\_optimization
If it is set to true, prevent scalar subqueries from (de)serializing large scalar values and possibly avoid running the same subquery more than once.
enable\_scopes\_for\_with\_statement
If disabled, declarations in parent WITH cluases will behave the same scope as they declared in the current scope.
Note that this is a compatibility setting for the analyzer to allow running some invalid queries that old analyzer could execute.
enable\_sharding\_aggregator
Enables sharded `GROUP BY` optimization that distributes rows across threads by hashing the grouping key, so each thread aggregates a disjoint subset of keys without a merge phase.
This is efficient for high-cardinality keys with evenly distributed data, but may suffer from highly skewed key distributions or queries with very few distinct keys.
Possible values:
* 0 — Sharded aggregation optimization is disabled.
* 1 — Sharded aggregation optimization is enabled.
enable\_shared\_storage\_snapshot\_in\_query
If enabled, all subqueries within a single query will share the same StorageSnapshot for each table.
This ensures a consistent view of the data across the entire query, even if the same table is accessed multiple times.
This is required for queries where internal consistency of data parts is important. Example:
```sql theme={null}
SELECT
count()
FROM events
WHERE (_part, _part_offset) IN (
SELECT _part, _part_offset
FROM events
WHERE user_id = 42
)
```
Without this setting, the outer and inner queries may operate on different data snapshots, leading to incorrect results.
Enabling this setting disables the optimization which removes unnecessary data parts from snapshots once the planning stage is complete.
As a result, long-running queries may hold onto obsolete parts for their entire duration, delaying part cleanup and increasing storage pressure.
This setting currently applies only to tables from the MergeTree family.
Possible values:
* 0 - Disabled
* 1 - Enabled
enable\_sharing\_sets\_for\_mutations
Allow sharing set objects build for IN subqueries between different tasks of the same mutation. This reduces memory usage and CPU consumptio
enable\_streaming\_queries
Allow `SELECT ... FROM t STREAM [CURSOR '{...}']` continuous queries.
When off, any table expression using the `STREAM` modifier is rejected
at plan-build time. This is the umbrella gate for the streaming-queries
feature; additional capabilities may be gated by their own settings.
enable\_time\_time64\_type
**Aliases**: `allow_experimental_time_time64_type`
Allows creation of [Time](/docs/reference/data-types/time) and [Time64](/docs/reference/data-types/time64) data types.
enable\_unaligned\_array\_join
Allow ARRAY JOIN with multiple arrays that have different sizes. When this settings is enabled, arrays will be resized to the longest one.
enable\_url\_encoding
Allows to enable/disable decoding/encoding path in uri in [URL](/docs/reference/engines/table-engines/special/url) engine tables.
Disabled by default.
enable\_vertical\_final
If enable, remove duplicated rows during FINAL by marking rows as deleted and filtering them later instead of merging rows
enable\_writes\_to\_query\_cache
If turned on, results of `SELECT` queries are stored in the [query cache](/docs/concepts/features/performance/caches/query-cache).
Possible values:
* 0 - Disabled
* 1 - Enabled