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47 lines
2.1 KiB
Markdown
47 lines
2.1 KiB
Markdown
<a name="dicts-external_dicts"></a>
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# External dictionaries
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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#dicts-external_dicts_dict_sources)".
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ClickHouse:
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> - Fully or partially stores dictionaries in RAM.
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- Periodically updates dictionaries and dynamically loads missing values. In other words, dictionaries can be loaded dynamically.
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The configuration of external dictionaries is located in one or more files. The path to the configuration is specified in the [dictionaries_config](../operations/server_settings/settings.md#server_settings-dictionaries_config) parameter.
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Dictionaries can be loaded at server startup or at first use, depending on the [dictionaries_lazy_load](../operations/server_settings/settings.md#server_settings-dictionaries_lazy_load) setting.
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The dictionary config file has the following format:
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```xml
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<yandex>
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<comment>An optional element with any content. Ignored by the ClickHouse server.</comment>
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<!--Optional element. File name with substitutions-->
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<include_from>/etc/metrika.xml</include_from>
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<dictionary>
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<!-- Dictionary configuration -->
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</dictionary>
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...
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<dictionary>
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<!-- Dictionary configuration -->
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</dictionary>
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</yandex>
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```
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You can [configure](external_dicts_dict.md#dicts-external_dicts_dict) any number of dictionaries in the same file. The file format is preserved even if there is only one dictionary (i.e. `<yandex><dictionary> <!--configuration -> </dictionary></yandex>` ).
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See also "[Functions for working with external dictionaries](../functions/ext_dict_functions.md#ext_dict_functions)".
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<div class="admonition attention">
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You can convert values for a small dictionary by describing it in a `SELECT` query (see the [transform](../functions/other_functions.md#other_functions-transform) function). This functionality is not related to external dictionaries.
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</div>
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