adriangb opened a new pull request, #23397: URL: https://github.com/apache/datafusion/pull/23397
## Which issue does this PR close? - Related to https://github.com/apache/datafusion-comet/issues/4859. Second of a 3-PR stack: #23396 (refactor), this benchmark, and the feature PR (nested schema pruning for the parquet reader). ## Rationale for this change When a table's declared schema is narrower than a parquet file's nested column (logical `events: LIST<STRUCT<x, y>>` over a physical `LIST<STRUCT<x, y, +8 pads>>`), the reader currently fetches and decodes **every** leaf of the column and discards the extra subfields in memory via the adapter-inserted cast. This is how engines like Spark (via Comet) communicate nested projection pruning to the scan — as a clipped read schema — and it is where Comet measured reading 1.35 TB where Spark read 30.9 GB for the same pruned `ReadSchema`. This PR adds a benchmark that documents the current behavior as a checked-in baseline, independent of any fix: ``` list_struct_narrow_schema: bytes_scanned=25.19 MB 3.45 ms list_struct_full_schema: bytes_scanned=25.19 MB 3.36 ms <- narrow == full today list_struct_physically_narrow: bytes_scanned= 3.32 KB 164 µs <- the floor ``` ## What changes are included in this PR? A criterion benchmark, `datafusion/core/benches/parquet_nested_schema_pruning.rs`, that registers the same wide `list<struct>` (and top-level struct) parquet file with both its full schema and a narrower declared schema, plus a physically-narrow file as the floor, and prints the scans' `bytes_scanned` at setup so the IO pattern is visible alongside wall time. ## Are these changes tested? It is a benchmark; it compiles under `cargo bench --no-run` and runs green. ## Are there any user-facing changes? No. 🤖 Generated with [Claude Code](https://claude.com/claude-code) https://claude.ai/code/session_01KuMaRtFSPDQesuzjN5Koyd -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
