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64a892c0e6
This addresses one of the remarks in the PR. All format schemas are required to be in the <format_schema_path> directory. This makes loading schema files less tedious, as the path can be omitted.
30 lines
1.1 KiB
ReStructuredText
30 lines
1.1 KiB
ReStructuredText
CapnProto
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---------
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Cap'n Proto is a binary message format. Like Protocol Buffers and Thrift (but unlike JSON or MessagePack), Cap'n Proto messages are strongly-typed and not self-describing. Due to this, it requires a ``schema`` setting to specify schema file and the root object. The schema is parsed on runtime and cached for each SQL statement.
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.. code-block:: 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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When the `schema.capnp` schema file looks like:
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.. code-block:: text
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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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The schema files are located in the path specified in the configuration file:
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.. code-block:: xml
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<!-- Directory containing schema files for various input formats. -->
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<format_schema_path>format_schemas/</format_schema_path>
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Deserialization is almost as efficient as the binary rows format, with typically zero allocation overhead per message.
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You can use this format as an efficient exchange message format in your data processing pipeline.
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