ClickHouse/docs/en/operations/system-tables/dictionaries.md

# system.dictionaries {#system_tables-dictionaries}

Contains information about [external dictionaries](../../sql-reference/dictionaries/external-dictionaries/external-dicts.md).

Columns:

-   `database` ([String](../../sql-reference/data-types/string.md)) — Name of the database containing the dictionary created by DDL query. Empty string for other dictionaries.
-   `name` ([String](../../sql-reference/data-types/string.md)) — [Dictionary name](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict.md).
-   `uuid` ([UUID](../../sql-reference/data-types/uuid.md)) — Dictionary UUID.
-   `status` ([Enum8](../../sql-reference/data-types/enum.md)) — Dictionary status. Possible values:
    -   `NOT_LOADED` — Dictionary was not loaded because it was not used.
    -   `LOADED` — Dictionary loaded successfully.
    -   `FAILED` — Unable to load the dictionary as a result of an error.
    -   `LOADING` — Dictionary is loading now.
    -   `LOADED_AND_RELOADING` — Dictionary is loaded successfully, and is being reloaded right now (frequent reasons: [SYSTEM RELOAD DICTIONARY](../../sql-reference/statements/system.md#query_language-system-reload-dictionary) query, timeout, dictionary config has changed).
    -   `FAILED_AND_RELOADING` — Could not load the dictionary as a result of an error and is loading now.
-   `origin` ([String](../../sql-reference/data-types/string.md)) — Path to the configuration file that describes the dictionary.
-   `type` ([String](../../sql-reference/data-types/string.md)) — Type of a dictionary allocation. [Storing Dictionaries in Memory](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-layout.md).
-   `key.names` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — Array of [key names](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md#ext_dict_structure-key) provided by the dictionary.
-   `key.types` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — Corresponding array of [key types](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md#ext_dict_structure-key) provided by the dictionary.
-   `attribute.names` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — Array of [attribute names](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md#ext_dict_structure-attributes) provided by the dictionary.
-   `attribute.types` ([Array](../../sql-reference/data-types/array.md)([String](../../sql-reference/data-types/string.md))) — Corresponding array of [attribute types](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md#ext_dict_structure-attributes) provided by the dictionary.
-   `bytes_allocated` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Amount of RAM allocated for the dictionary.
-   `query_count` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Number of queries since the dictionary was loaded or since the last successful reboot.
-   `hit_rate` ([Float64](../../sql-reference/data-types/float.md)) — For cache dictionaries, the percentage of uses for which the value was in the cache.
-   `found_rate` ([Float64](../../sql-reference/data-types/float.md)) — The percentage of uses for which the value was found.
-   `element_count` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Number of items stored in the dictionary.
-   `load_factor` ([Float64](../../sql-reference/data-types/float.md)) — Percentage filled in the dictionary (for a hashed dictionary, the percentage filled in the hash table).
-   `source` ([String](../../sql-reference/data-types/string.md)) — Text describing the [data source](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md) for the dictionary.
-   `lifetime_min` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Minimum [lifetime](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-lifetime.md) of the dictionary in memory, after which ClickHouse tries to reload the dictionary (if `invalidate_query` is set, then only if it has changed). Set in seconds.
-   `lifetime_max` ([UInt64](../../sql-reference/data-types/int-uint.md#uint-ranges)) — Maximum [lifetime](../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-lifetime.md) of the dictionary in memory, after which ClickHouse tries to reload the dictionary (if `invalidate_query` is set, then only if it has changed). Set in seconds.
-   `loading_start_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — Start time for loading the dictionary.
-   `last_successful_update_time` ([DateTime](../../sql-reference/data-types/datetime.md)) — End time for loading or updating the dictionary. Helps to monitor some troubles with external sources and investigate causes.
-   `loading_duration` ([Float32](../../sql-reference/data-types/float.md)) — Duration of a dictionary loading.
-   `last_exception` ([String](../../sql-reference/data-types/string.md)) — Text of the error that occurs when creating or reloading the dictionary if the dictionary couldn’t be created.
-   `comment` ([String](../../sql-reference/data-types/string.md)) — Text of the comment to dictionary.

**Example**

Configure the dictionary:

``` sql
CREATE DICTIONARY dictionary_with_comment
(
    id UInt64,
    value String
)
PRIMARY KEY id
SOURCE(CLICKHOUSE(HOST 'localhost' PORT tcpPort() TABLE 'source_table'))
LAYOUT(FLAT())
LIFETIME(MIN 0 MAX 1000)
COMMENT 'The temporary dictionary';
```

Make sure that the dictionary is loaded.

``` sql
SELECT * FROM system.dictionaries LIMIT 1 FORMAT Vertical;
```

``` text
Row 1:
──────
database:                    default
name:                        dictionary_with_comment
uuid:                        4654d460-0d03-433a-8654-d4600d03d33a
status:                      NOT_LOADED
origin:                      4654d460-0d03-433a-8654-d4600d03d33a
type:
key.names:                   ['id']
key.types:                   ['UInt64']
attribute.names:             ['value']
attribute.types:             ['String']
bytes_allocated:             0
query_count:                 0
hit_rate:                    0
found_rate:                  0
element_count:               0
load_factor:                 0
source:
lifetime_min:                0
lifetime_max:                0
loading_start_time:          1970-01-01 00:00:00
last_successful_update_time: 1970-01-01 00:00:00
loading_duration:            0
last_exception:
comment:                     The temporary dictionary
```