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

system.dictionaries

Contains information about external dictionaries.

Columns:

• database (String) — Name of the database containing the dictionary created by DDL query. Empty string for other dictionaries.
• name (String) — Dictionary name.
• uuid (UUID) — Dictionary UUID.
• status (Enum8) — 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 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) — Path to the configuration file that describes the dictionary.
• type (String) — Type of a dictionary allocation. Storing Dictionaries in Memory.
• key.names (Array(String)) — Array of key names provided by the dictionary.
• key.types (Array(String)) — Corresponding array of key types provided by the dictionary.
• attribute.names (Array(String)) — Array of attribute names provided by the dictionary.
• attribute.types (Array(String)) — Corresponding array of attribute types provided by the dictionary.
• bytes_allocated (UInt64) — Amount of RAM allocated for the dictionary.
• query_count (UInt64) — Number of queries since the dictionary was loaded or since the last successful reboot.
• hit_rate (Float64) — For cache dictionaries, the percentage of uses for which the value was in the cache.
• found_rate (Float64) — The percentage of uses for which the value was found.
• element_count (UInt64) — Number of items stored in the dictionary.
• load_factor (Float64) — Percentage filled in the dictionary (for a hashed dictionary, the percentage filled in the hash table).
• source (String) — Text describing the data source for the dictionary.
• lifetime_min (UInt64) — Minimum lifetime 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) — Maximum lifetime 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) — Start time for loading the dictionary.
• last_successful_update_time (DateTime) — End time for loading or updating the dictionary. Helps to monitor some troubles with external sources and investigate causes.
• loading_duration (Float32) — Duration of a dictionary loading.
• last_exception (String) — Text of the error that occurs when creating or reloading the dictionary if the dictionary couldn’t be created.
• comment (String) — Text of the comment to dictionary.

Example

Configure the dictionary:

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.

SELECT * FROM system.dictionaries LIMIT 1 FORMAT Vertical;

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