ClickHouse/docs/en/system_tables/system.dictionaries.md
2018-03-26 17:00:55 +03:00

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system.dictionaries

Contains information about external dictionaries.

Columns:

name String                   Dictionary name.
type String                   Dictionary type: Flat, Hashed, Cache.
origin String                 Path to the config file where the dictionary is described.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.
has_hierarchy UInt8           Whether the dictionary is hierarchical.
bytes_allocated UInt64         The amount of RAM used by the dictionary.
hit_rate Float64               For cache dictionaries, the percent of usage for which the value was in the cache.
element_count UInt64           The number of items stored in the dictionary.
load_factor Float64           The filled percentage of the dictionary (for a hashed dictionary, it is the filled percentage of the hash table).
creation_time DateTime         Time spent for the creation or last successful reload of the dictionary.
last_exception String         Text of an error that occurred when creating or reloading the dictionary, if the dictionary couldn't be created.
source String                 Text describing the data source for the dictionary.

Note that the amount of memory used by the dictionary is not proportional to the number of items stored in it. So for flat and cached dictionaries, all the memory cells are pre-assigned, regardless of how full the dictionary actually is.