mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-10-08 01:20:55 +00:00
d91c97d15d
* Replace underscores with hyphens * remove temporary code * fix style check * fix collapse
55 lines
2.8 KiB
Markdown
55 lines
2.8 KiB
Markdown
---
|
||
toc_priority: 39
|
||
toc_title: General Description
|
||
---
|
||
|
||
# External Dictionaries {#dicts-external-dicts}
|
||
|
||
You can add your own dictionaries from various data sources. The data source for a dictionary can be a local text or executable file, an HTTP(s) resource, or another DBMS. For more information, see “[Sources for external dictionaries](external-dicts-dict-sources.md)”.
|
||
|
||
ClickHouse:
|
||
|
||
- Fully or partially stores dictionaries in RAM.
|
||
- Periodically updates dictionaries and dynamically loads missing values. In other words, dictionaries can be loaded dynamically.
|
||
- Allows to create external dictionaries with xml files or [DDL queries](../../statements/create.md#create-dictionary-query).
|
||
|
||
The configuration of external dictionaries can be located in one or more xml-files. The path to the configuration is specified in the [dictionaries\_config](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_config) parameter.
|
||
|
||
Dictionaries can be loaded at server startup or at first use, depending on the [dictionaries\_lazy\_load](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_lazy_load) setting.
|
||
|
||
The dictionary configuration file has the following format:
|
||
|
||
``` xml
|
||
<yandex>
|
||
<comment>An optional element with any content. Ignored by the ClickHouse server.</comment>
|
||
|
||
<!--Optional element. File name with substitutions-->
|
||
<include_from>/etc/metrika.xml</include_from>
|
||
|
||
|
||
<dictionary>
|
||
<!-- Dictionary configuration. -->
|
||
<!-- There can be any number of <dictionary> sections in the configuration file. -->
|
||
</dictionary>
|
||
|
||
</yandex>
|
||
```
|
||
|
||
You can [configure](external-dicts-dict.md) any number of dictionaries in the same file.
|
||
|
||
[DDL queries for dictionaries](../../statements/create.md#create-dictionary-query) doesn’t require any additional records in server configuration. They allow to work with dictionaries as first-class entities, like tables or views.
|
||
|
||
!!! attention "Attention"
|
||
You can convert values for a small dictionary by describing it in a `SELECT` query (see the [transform](../../../sql-reference/functions/other-functions.md) function). This functionality is not related to external dictionaries.
|
||
|
||
## See Also {#ext-dicts-see-also}
|
||
|
||
- [Configuring an External Dictionary](external-dicts-dict.md)
|
||
- [Storing Dictionaries in Memory](external-dicts-dict-layout.md)
|
||
- [Dictionary Updates](external-dicts-dict-lifetime.md)
|
||
- [Sources of External Dictionaries](external-dicts-dict-sources.md)
|
||
- [Dictionary Key and Fields](external-dicts-dict-structure.md)
|
||
- [Functions for Working with External Dictionaries](../../../sql-reference/functions/ext-dict-functions.md)
|
||
|
||
[Original article](https://clickhouse.tech/docs/en/query_language/dicts/external_dicts/) <!--hide-->
|