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27 lines
893 B
Markdown
27 lines
893 B
Markdown
<a name="format_capnproto"></a>
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# CapnProto
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Cap'n Proto is a binary message format similar to Protocol Buffers and Thrift, but not like JSON or MessagePack.
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Cap'n Proto messages are strictly typed and not self-describing, meaning they need an external schema description. The schema is applied on the fly and cached for each query.
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```sql
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SELECT SearchPhrase, count() AS c FROM test.hits
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GROUP BY SearchPhrase FORMAT CapnProto SETTINGS schema = 'schema:Message'
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```
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Where `schema.capnp` looks like this:
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```
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struct Message {
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SearchPhrase @0 :Text;
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c @1 :Uint64;
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}
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```
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Schema files are in the file that is located in the directory specified in [ format_schema_path](../operations/server_settings/settings.md#server_settings-format_schema_path) in the server configuration.
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Deserialization is effective and usually doesn't increase the system load.
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