mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-17 13:13:36 +00:00
27 lines
867 B
Markdown
Executable File
27 lines
867 B
Markdown
Executable File
<a name="format_capnproto"></a>
|
|
|
|
# CapnProto
|
|
|
|
Cap'n Proto is a binary message format similar to Protocol Buffers and Thrift, but not like JSON or MessagePack.
|
|
|
|
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.
|
|
|
|
```sql
|
|
SELECT SearchPhrase, count() AS c FROM test.hits
|
|
GROUP BY SearchPhrase FORMAT CapnProto SETTINGS schema = 'schema:Message'
|
|
```
|
|
|
|
Where `schema.capnp` looks like this:
|
|
|
|
```
|
|
struct Message {
|
|
SearchPhrase @0 :Text;
|
|
c @1 :Uint64;
|
|
}
|
|
```
|
|
|
|
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.
|
|
|
|
Deserialization is effective and usually doesn't increase the system load.
|
|
|