ClickHouse/clickhouse-docs-embeddings huggingface dataset:
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/s3_queue_settings.md)

Contains information about the settings of [S3Queue](/docs/engines/table-engines/integrations/s3queue) tables. Available from server version `24.10`.

Columns:

- `database` ([String](/docs/sql-reference/data-types)) — Database of the table with S3Queue Engine.
- `table` ([String](/docs/sql-reference/data-types)) — Name of the table with S3Queue Engine.
- `name` ([String](/docs/sql-reference/data-types)) — Setting name.
- `value` ([String](/docs/sql-reference/data-types)) — Setting value.
- `type` ([String](/docs/sql-reference/data-types)) — Setting type (implementation specific string value).
- `changed` ([UInt8](/docs/sql-reference/data-types)) — 1 if the setting was explicitly defined in the config or explicitly changed.
- `description` ([String](/docs/sql-reference/data-types)) — Setting description.
- `alterable` ([UInt8](/docs/sql-reference/data-types)) — Shows whether the current user can change the setting via ALTER TABLE MODIFY SETTING: 0 — Current user can change the setting, 1 — Current user can't change the setting.

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/settings_changes.md)

Contains information about setting changes in previous ClickHouse versions.

Columns:

- `type` ([Enum8('Session' = 0, 'MergeTree' = 1)](/docs/sql-reference/data-types)) — The group of settings (Session, MergeTree...)
- `version` ([String](/docs/sql-reference/data-types)) — The ClickHouse server version.
- `changes` ([Array(Tuple(name String, previous\_value String, new\_value String, reason String))](/docs/sql-reference/data-types)) — The list of changes in settings which changed the behaviour of ClickHouse.

**Example**

```
SELECT *
FROM system.settings_changes
WHERE version = '23.5'
FORMAT Vertical
```

```
Row 1:
──────
type:    Core
version: 23.5
changes: [('input_format_parquet_preserve_order','1','0','Allow Parquet reader to reorder rows for better parallelism.'),('parallelize_output_from_storages','0','1','Allow parallelism when executing queries that read from file/url/s3/etc. This may reorder rows.'),('use_with_fill_by_sorting_prefix','0','1','Columns preceding WITH FILL columns in ORDER BY clause form sorting prefix. Rows with different values in sorting prefix are filled independently'),('output_format_parquet_compliant_nested_types','0','1','Change an internal field name in output Parquet file schema.')]
```

**See also**

- [Settings](/docs/operations/system-tables/overview#system-tables-introduction)
- [system.settings](/docs/operations/system-tables/settings)

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/settings_profile_elements.md)

Describes the content of the settings profile:

- Сonstraints.
- Roles and users that the setting applies to.
- Parent settings profiles.

Columns:

- `profile_name` ([Nullable(String)](/docs/sql-reference/data-types)) — Setting profile name.
- `user_name` ([Nullable(String)](/docs/sql-reference/data-types)) — User name.
- `role_name` ([Nullable(String)](/docs/sql-reference/data-types)) — Role name.
- `index` ([UInt64](/docs/sql-reference/data-types)) — Sequential number of the settings profile element.
- `setting_name` ([Nullable(String)](/docs/sql-reference/data-types)) — Setting name.
- `value` ([Nullable(String)](/docs/sql-reference/data-types)) — Setting value.
- `min` ([Nullable(String)](/docs/sql-reference/data-types)) — The minimum value of the setting. NULL if not set.
- `max` ([Nullable(String)](/docs/sql-reference/data-types)) — The maximum value of the setting. NULL if not set.
- `writability` ([Nullable(Enum8('WRITABLE' = 0, 'CONST' = 1, 'CHANGEABLE\_IN\_READONLY' = 2))](/docs/sql-reference/data-types)) — The property which shows whether a setting can be changed or not.
- `inherit_profile` ([Nullable(String)](/docs/sql-reference/data-types)) — A parent profile for this setting profile. NULL if not set. Setting profile will inherit all the settings' values and constraints (min, max, readonly) from its parent profiles.

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/settings_profiles.md)

Contains properties of configured setting profiles.

Columns:

- `name` ([String](/docs/sql-reference/data-types)) — Setting profile name.
- `id` ([UUID](/docs/sql-reference/data-types)) — Setting profile ID.
- `storage` ([String](/docs/sql-reference/data-types)) — Path to the storage of setting profiles. Configured in the `access_control_path` parameter.
- `num_elements` ([UInt64](/docs/sql-reference/data-types)) — Number of elements for this profile in the `system.settings_profile_elements` table.
- `apply_to_all` ([UInt8](/docs/sql-reference/data-types)) — Shows that the settings profile set for all roles and/or users.
- `apply_to_list` ([Array(String)](/docs/sql-reference/data-types)) — List of the roles and/or users to which the setting profile is applied.
- `apply_to_except` ([Array(String)](/docs/sql-reference/data-types)) — The setting profile is applied to all roles and/or users excepting of the listed ones.

## See Also[​](#see-also "Direct link to See Also")

- [SHOW PROFILES](/docs/sql-reference/statements/show#show-profiles)

- [See Also](#see-also)

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/storage_policies.md)

Contains information about storage policies and volumes which are defined in [server configuration](/docs/engines/table-engines/mergetree-family/mergetree#table_engine-mergetree-multiple-volumes_configure).

Columns:

- `policy_name` ([String](/docs/sql-reference/data-types/string)) — Name of the storage policy.
- `volume_name` ([String](/docs/sql-reference/data-types/string)) — Volume name defined in the storage policy.
- `volume_priority` ([UInt64](/docs/sql-reference/data-types/int-uint)) — Volume order number in the configuration, the data fills the volumes according this priority, i.e. data during inserts and merges is written to volumes with a lower priority (taking into account other rules: TTL, `max_data_part_size`, `move_factor`).
- `disks` ([Array(String)](/docs/sql-reference/data-types/array)) — Disk names, defined in the storage policy.
- `volume_type` ([Enum8](/docs/sql-reference/data-types/enum)) — Type of volume. Can have one of the following values:
  - `JBOD`
  - `SINGLE_DISK`
  - `UNKNOWN`
- `max_data_part_size` ([UInt64](/docs/sql-reference/data-types/int-uint)) — Maximum size of a data part that can be stored on volume disks (0 — no limit).
- `move_factor` ([Float64](/docs/sql-reference/data-types/float)) — Ratio of free disk space. When the ratio exceeds the value of configuration parameter, ClickHouse start to move data to the next volume in order.
- `prefer_not_to_merge` ([UInt8](/docs/sql-reference/data-types/int-uint)) — Value of the `prefer_not_to_merge` setting. Should be always false. When this setting is enabled, you did a mistake.
- `perform_ttl_move_on_insert` ([UInt8](/docs/sql-reference/data-types/int-uint)) — Value of the `perform_ttl_move_on_insert` setting. — Disables TTL move on data part INSERT. By default if we insert a data part that already expired by the TTL move rule it immediately goes to a volume/disk declared in move rule. This can significantly slowdown insert in case if destination volume/disk is slow (e.g. S3).
- `load_balancing` ([Enum8](/docs/sql-reference/data-types/enum)) — Policy for disk balancing. Can have one of the following values:
  - `ROUND_ROBIN`
  - `LEAST_USED`

If the storage policy contains more then one volume, then information for each volume is stored in the individual row of the table.

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/symbols.md)

Contains information for introspection of `clickhouse` binary. It requires the introspection privilege to access.
This table is only useful for C++ experts and ClickHouse engineers.

Columns:

- `symbol` ([String](/docs/sql-reference/data-types/string)) — Symbol name in the binary. It is mangled. You can apply `demangle(symbol)` to obtain a readable name.
- `symbol_demangled` ([Nullable(String)](/docs/sql-reference/data-types/string)) — Demangled symbol used for XRay instrumentation.
- `function_id` ([Nullable(Int32)](/docs/sql-reference/data-types/int-uint)) — Function ID in the XRay instrumentation map.
- `address_begin` ([UInt64](/docs/sql-reference/data-types/int-uint)) — Start address of the symbol in the binary.
- `address_end` ([UInt64](/docs/sql-reference/data-types/int-uint)) — End address of the symbol in the binary.
- `name` ([String](/docs/sql-reference/data-types/string)) — Alias for `event`.

**Example**

```
SELECT * FROM system.symbols WHERE function_id IS NOT NULL LIMIT 5 SETTINGS allow_introspection_functions = 1
```

```
Row 1:
──────
symbol:           _Z15isClickhouseAppNSt3__117basic_string_viewIcNS_11char_traitsIcEEEERNS_6vectorIPcNS_9allocatorIS5_EEEE
symbol_demangled: isClickhouseApp(std::__1::basic_string_view<char, std::__1::char_traits<char>>, std::__1::vector<char*, std::__1::allocator<char*>>&)
function_id:      1
address_begin:    219229312 -- 219.23 million
address_end:      219231408 -- 219.23 million

Row 2:
──────
symbol:           main
symbol_demangled: main
function_id:      2
address_begin:    219231872 -- 219.23 million
address_end:      219233485 -- 219.23 million

Row 3:
──────
symbol:           _ZN12_GLOBAL__N_19printHelpEiPPc
symbol_demangled: (anonymous namespace)::printHelp(int, char**)
function_id:      3
address_begin:    219233536 -- 219.23 million
address_end:      219233902 -- 219.23 million

Row 4:
──────
symbol:           _ZNSt3__110filesystem4pathC2B8se210105IPcvEERKT_NS1_6formatE
symbol_demangled: std::__1::filesystem::path::path[abi:se210105]<char*, void>(char* const&, std::__1::filesystem::path::format)
function_id:      4
address_begin:    219234496 -- 219.23 million
address_end:      219234620 -- 219.23 million

Row 5:
──────
symbol:           _ZNSt3__113unordered_setINS_17basic_string_viewIcNS_11char_traitsIcEEEENS_4hashIS4_EENS_8equal_toIS4_EENS_9allocatorIS4_EEEC2ESt16initializer_listIS4_E
symbol_demangled: std::__1::unordered_set<std::__1::basic_string_view<char, std::__1::char_traits<char>>, std::__1::hash<std::__1::basic_string_view<char, std::__1::char_traits<char>>>, std::__1::equal_to<std::__1::basic_string_view<char, std::__1::char_traits<char>>>, std::__1::allocator<std::__1::basic_string_view<char, std::__1::char_traits<char>>>>::unordered_set(std::initializer_list<std::__1::basic_string_view<char, std::__1::char_traits<char>>>)
function_id:      5
address_begin:    219235584 -- 219.24 million
address_end:      219235708 -- 219.24 million
```

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/error_log.md)

Querying in ClickHouse Cloud

The data in this system table is held locally on each node in ClickHouse Cloud. Obtaining a complete view of all data, therefore, requires the `clusterAllReplicas` function. See [here](/docs/operations/system-tables/overview#system-tables-in-clickhouse-cloud) for further details.

Contains history of error values from table `system.errors`, periodically flushed to disk.

Columns:

- `hostname` ([LowCardinality(String)](/docs/sql-reference/data-types/string)) — Hostname of the server executing the query.
- `event_date` ([Date](/docs/sql-reference/data-types/date)) — Event date.
- `event_time` ([DateTime](/docs/sql-reference/data-types/datetime)) — Event time.
- `code` ([Int32](/docs/sql-reference/data-types/int-uint)) — Code number of the error.
- `error` ([LowCardinality(String)](/docs/sql-reference/data-types/string)) - Name of the error.
- `value` ([UInt64](/docs/sql-reference/data-types/int-uint)) — The number of times this error happened.
- `remote` ([UInt8](/docs/sql-reference/data-types/int-uint)) — Remote exception (i.e. received during one of the distributed queries).
- `last_error_time` ([DateTime](/docs/sql-reference/data-types/datetime)) — The time when the last error happened.
- `last_error_message` ([String](/docs/sql-reference/data-types/string)) — Message for the last error.
- `last_error_query_id` ([String](/docs/sql-reference/data-types/string)) — Id of a query that caused the last error (if available).
- `last_error_trace` ([Array(UInt64)](/docs/sql-reference/data-types/array)) — A stack trace that represents a list of physical addresses where the called methods are stored.

**Example**

```
SELECT * FROM system.error_log LIMIT 1 FORMAT Vertical;
```

```
Row 1:
──────
hostname:            clickhouse.testing.internal
event_date:          2025-11-11
event_time:          2025-11-11 11:35:28
code:                60
error:               UNKNOWN_TABLE
value:               1
remote:              0
last_error_time:     2025-11-11 11:35:28
last_error_message:  Unknown table expression identifier 'system.table_not_exist' in scope SELECT * FROM system.table_not_exist
last_error_query_id: 77ad9ece-3db7-4236-9b5a-f789bce4aa2e
last_error_trace:    [100506790044914,100506534488542,100506409937998,100506409936517,100506425182891,100506618154123,100506617994473,100506617990486,100506617988112,100506618341386,100506630272160,100506630266232,100506630276900,100506629795243,100506633519500,100506633495783,100506692143858,100506692248921,100506790779783,100506790781278,100506790390399,100506790380047,123814948752036,123814949330028]
```

**See also**

- [error\_log setting](/docs/operations/server-configuration-parameters/settings#error_log) — Enabling and disabling the setting.
- [system.errors](/docs/operations/system-tables/errors) — Contains error codes with the number of times they have been triggered.
- [Monitoring](/docs/operations/monitoring) — Base concepts of ClickHouse monitoring.

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/system_warnings.md)

Querying in ClickHouse Cloud

The data in this system table is held locally on each node in ClickHouse Cloud. Obtaining a complete view of all data, therefore, requires the `clusterAllReplicas` function. See [here](/docs/operations/system-tables/overview#system-tables-in-clickhouse-cloud) for further details.

This table shows warnings about the ClickHouse server.
Warnings of the same type are combined into a single warning.
For example, if the number N of attached databases exceeds a configurable threshold T, a single entry containing the current value N is shown instead of N separate entries.
If current value drops below the threshold, the entry is removed from the table.

The table can be configured with these settings:

- [max\_table\_num\_to\_warn](/docs/operations/server-configuration-parameters/settings#max_table_num_to_warn)
- [max\_database\_num\_to\_warn](/docs/operations/server-configuration-parameters/settings#max_database_num_to_warn)
- [max\_dictionary\_num\_to\_warn](/docs/operations/server-configuration-parameters/settings#max_dictionary_num_to_warn)
- [max\_view\_num\_to\_warn](/docs/operations/server-configuration-parameters/settings#max_view_num_to_warn)
- [max\_part\_num\_to\_warn](/docs/operations/server-configuration-parameters/settings#max_part_num_to_warn)
- [max\_pending\_mutations\_to\_warn](/docs/operations/server-configuration-parameters/settings#max_pending_mutations_to_warn)
- [max\_pending\_mutations\_execution\_time\_to\_warn](/docs/operations/server-configuration-parameters/settings#max_pending_mutations_execution_time_to_warn)
- [max\_named\_collection\_num\_to\_warn](/docs/operations/server-configuration-parameters/settings#max_named_collection_num_to_warn)
- [resource\_overload\_warnings](/docs/operations/settings/server-overload#resource-overload-warnings)

Columns:

- `message` ([String](/docs/sql-reference/data-types/string)) — Warning message.
- `message_format_string` ([LowCardinality(String)](/docs/sql-reference/data-types/string)) — The format string used to format the message.

**Example**

Query:

```
 SELECT * FROM system.warnings LIMIT 2 \G;
```

Result:

```
Row 1:
──────
message:               The number of active parts is more than 10.
message_format_string: The number of active parts is more than {}.

Row 2:
──────
message:               The number of attached databases is more than 2.
message_format_string: The number of attached databases is more than {}.
```

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/table_engines.md)

Contains description of table engines supported by server and their feature support information.

This table contains the following columns (the column type is shown in brackets):

- `name` ([String](/docs/sql-reference/data-types)) — The name of table engine.
- `supports_settings` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates if table engine supports SETTINGS clause.
- `supports_skipping_indices` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates if table engine supports skipping indices.
- `supports_projections` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicated if table engine supports projections.
- `supports_sort_order` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates if table engine supports clauses PARTITION\_BY, PRIMARY\_KEY, ORDER\_BY and SAMPLE\_BY.
- `supports_ttl` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates if table engine supports TTL.
- `supports_replication` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates if table engine supports data replication.
- `supports_deduplication` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates if table engine supports data deduplication.
- `supports_parallel_insert` ([UInt8](/docs/sql-reference/data-types)) — Flag that indicates if table engine supports parallel insert (see max\_insert\_threads setting).

Example:

```
SELECT *
FROM system.table_engines
WHERE name IN ('Kafka', 'MergeTree', 'ReplicatedCollapsingMergeTree')
```

```
┌─name──────────────────────────┬─supports_settings─┬─supports_skipping_indices─┬─supports_sort_order─┬─supports_ttl─┬─supports_replication─┬─supports_deduplication─┬─supports_parallel_insert─┐
│ MergeTree                     │                 1 │                         1 │                   1 │            1 │                    0 │                      0 │                        1 │
│ Kafka                         │                 1 │                         0 │                   0 │            0 │                    0 │                      0 │                        0 │
│ ReplicatedCollapsingMergeTree │                 1 │                         1 │                   1 │            1 │                    1 │                      1 │                        1 │
└───────────────────────────────┴───────────────────┴───────────────────────────┴─────────────────────┴──────────────┴──────────────────────┴────────────────────────┴──────────────────────────┘
```

**See also**

- MergeTree family [query clauses](/docs/engines/table-engines/mergetree-family/mergetree#mergetree-query-clauses)
- Kafka [settings](/docs/engines/table-engines/integrations/kafka#creating-a-table)
- Join [settings](/docs/engines/table-engines/special/join#join-limitations-and-settings)

Was this page helpful?
title_wip

Row 2:
──────
database:                   default
name:                       53r93yleapyears
uuid:                       00000000-0000-0000-0000-000000000000
engine:                     MergeTree
is_temporary:               0
data_paths:                 ['/var/lib/clickhouse/data/default/53r93yleapyears/']
metadata_path:              /var/lib/clickhouse/metadata/default/53r93yleapyears.sql
metadata_modification_time: 2020-09-23 09:05:36
dependencies_database:      []
dependencies_table:         []
create_table_query:         CREATE TABLE default.`53r93yleapyears` (`id` Int8, `febdays` Int8) ENGINE = MergeTree ORDER BY id
engine_full:                MergeTree ORDER BY id
as_select:                  SELECT name AS catalog_name
partition_key:
sorting_key:                id
primary_key:                id
sampling_key:
storage_policy:             default
total_rows:                 2
total_bytes:                155
lifetime_rows:              ᴺᵁᴸᴸ
lifetime_bytes:             ᴺᵁᴸᴸ
comment:
has_own_data:               0
loading_dependencies_database: []
loading_dependencies_table:    []
loading_dependent_database:    []
loading_dependent_table:       []
```

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/time_zones.md)

Contains a list of time zones that are supported by the ClickHouse server. This list of timezones might vary depending on the version of ClickHouse.

Columns:

- `time_zone` ([String](/docs/sql-reference/data-types)) — List of supported time zones.

**Example**

```
SELECT * FROM system.time_zones LIMIT 10
```

```
┌─time_zone──────────┐
│ Africa/Abidjan     │
│ Africa/Accra       │
│ Africa/Addis_Ababa │
│ Africa/Algiers     │
│ Africa/Asmara      │
│ Africa/Asmera      │
│ Africa/Bamako      │
│ Africa/Bangui      │
│ Africa/Banjul      │
│ Africa/Bissau      │
└────────────────────┘
```

Was this page helpful?
title_wip

[Edit this page](https://github.com/ClickHouse/ClickHouse/tree/master/docs/en/operations/system-tables/user_processes.md)

Querying in ClickHouse Cloud

The data in this system table is held locally on each node in ClickHouse Cloud. Obtaining a complete view of all data, therefore, requires the `clusterAllReplicas` function. See [here](/docs/operations/system-tables/overview#system-tables-in-clickhouse-cloud) for further details.

This system table can be used to get overview of memory usage and ProfileEvents of users.

Columns:

- `user` ([String](/docs/sql-reference/data-types)) — User name.
- `memory_usage` ([Int64](/docs/sql-reference/data-types)) — Sum of RAM used by all processes of the user. It might not include some types of dedicated memory. See the max\_memory\_usage setting.
- `peak_memory_usage` ([Int64](/docs/sql-reference/data-types)) — The peak of memory usage of the user. It can be reset when no queries are run for the user.
- `ProfileEvents` ([Map(LowCardinality(String), UInt64)](/docs/sql-reference/data-types)) — Summary of ProfileEvents that measure different metrics for the user. The description of them could be found in the table system.events

```
SELECT * FROM system.user_processes LIMIT 10 FORMAT Vertical;
```

```
Row 1:
──────
user:              default
memory_usage:      9832
peak_memory_usage: 9832
ProfileEvents:     {'Query':5,'SelectQuery':5,'QueriesWithSubqueries':38,'SelectQueriesWithSubqueries':38,'QueryTimeMicroseconds':842048,'SelectQueryTimeMicroseconds':842048,'ReadBufferFromFileDescriptorRead':6,'ReadBufferFromFileDescriptorReadBytes':234,'IOBufferAllocs':3,'IOBufferAllocBytes':98493,'ArenaAllocChunks':283,'ArenaAllocBytes':1482752,'FunctionExecute':670,'TableFunctionExecute':16,'DiskReadElapsedMicroseconds':19,'NetworkSendElapsedMicroseconds':684,'NetworkSendBytes':139498,'SelectedRows':6076,'SelectedBytes':685802,'ContextLock':1140,'RWLockAcquiredReadLocks':193,'RWLockReadersWaitMilliseconds':4,'RealTimeMicroseconds':1585163,'UserTimeMicroseconds':889767,'SystemTimeMicroseconds':13630,'SoftPageFaults':1947,'OSCPUWaitMicroseconds':6,'OSCPUVirtualTimeMicroseconds':903251,'OSReadChars':28631,'OSWriteChars':28888,'QueryProfilerRuns':3,'LogTrace':79,'LogDebug':24}

1 row in set. Elapsed: 0.010 sec.
```

Was this page helpful?