append transaction data path #390
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zachschuermann
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Nov 8, 2024
This PR is the second (of two) major pieces for supporting simple blind appends. It implements: 1. **new `Transaction` APIs** for appending data to delta tables: a. `get_write_context()` to get a `WriteContext` to pass to the data path which includes all information needed to write: `target directory`, `snapshot schema`, `transformation expression`, and (future: columns to collect stats on) b. `add_write_metadata(impl EngineData)` to add metadata about a write to the transaction along with a new static method `transaction::get_write_metadata_schema` to provide the expected schema of this engine data. c. new machinery in 'commit' method to commit new `Add` actions for each row of write_metadata from the API above. 2. **new default engine capabilities** for using the default engine to write parquet data (to append to tables): a. parquet handler can now `write_parquet_file(EngineData)` b. usage example in `write.rs` tests for now 3. **new append tests** in the `write.rs` integration test suite Details and some follow-ups: - the parquet writing (similar to JSON) currently just buffers everything into memory before issuing one big PUT. we should make this smarter: single PUT for small data and MultipartUpload for larger data. tracking in #418 - schema enforcement is done at the data layer. this means it is up to the engine to call the expression evaluation and we expect this to fail if the output schema is incorrect (see `test_append_invalid_schema` in `write.rs` integration test). we may want to change this in the future to eagerly error based on the engine providing a schema up front at metadata time (transaction creation time) based on #370 resolves #390
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