Isolate Avro usage in parquet-cli to commands that require Avro

[kevinjqliu]

Motivation

parquet-cli still uses Avro as an internal row model in places where users are only trying to inspect Parquet files. Valid Parquet is not always valid Avro, so Parquet inspection should not require Parquet schemas or records to round-trip through Avro.

cat/head already has a group-reader fallback for one class of problem: Avro schema conversion failures such as invalid Avro field names. That fallback is useful, but it is still a special case. Other inspection paths, such as scan, still use the Avro-backed data path for Parquet input.

Concrete examples:

• Invalid Avro field names: original-instruction and column with known type are valid Parquet field names but invalid Avro names. This already required a cat/head group-reader fallback.
• Nested Parquet structures: data/nested_lists.snappy.parquet is a valid parquet-testing fixture, but cat and scan fail through the Avro-backed reader.
• Projection/type mismatch: UUID and INT96 Parquet columns can fail when Avro projection rewrites the requested physical type.
• Lost Parquet structure: shredded Variant and other newer logical types can have valid Parquet physical structures that Avro cannot represent without losing information.

Avro is still part of the CLI API for conversion workflows. The goal is not to remove Avro; it is to stop requiring Avro for Parquet inspection.

Proposal

Use Avro only when the command or input/output format requires it. Use Parquet-native readers and metadata APIs for Parquet inspection and physical rewrites.

Command	Avro needed?	Proposed internal path
help, version	No	CLI metadata only
meta, pages, dictionary, check-stats, column-index, column-size, footer, bloom-filter, size-stats, geospatial-stats	No	ParquetFileReader and Parquet metadata/page/stat APIs
prune, trans-compression, masking, rewrite	No	Parquet rewrite utilities
cat, head	Only for non-Parquet inputs	Parquet -> GroupReadSupport; Avro/JSON -> Avro path
scan	Only for non-Parquet inputs	Parquet -> GroupReadSupport; Avro/JSON -> Avro path
schema	Yes by default	Keep Avro schema output; keep physical Parquet path for --parquet
csv-schema	Yes	Avro schema inference
convert-csv	Yes	CSV -> Avro records/schema -> Parquet
convert	Yes	Avro-backed conversion path
to-avro	Yes	Avro writer/schema path

Related issues

• Problem with a cat #2836 / GH-2836: Support reading pure parquet files with cat #3332: cat failed because Avro rejected a Parquet field name. The merged fix added a Parquet group-reader fallback.
• Issues when using the head on a parquet file #2835: head reported the same class of invalid Avro field-name failure.
• parquet-cli fails at supporting parquet-protobuf generated files #2708: cat failed on parquet-protobuf files with modern LIST encoding via AvroRecordConverter.
• parquet-cli unable to read UUID values #1641: UUID values failed because Avro projection changed the requested physical type; skipping projection let the file read.
• parquet-cli cannot display data containing int96 type #3345: INT96 data failed through Avro requested-schema conversion.
• AvroSchemaConverter silently drops typed_value when converting shredded variant schemas #3477: Avro schema conversion dropped typed_value from shredded Variant schemas.
• Make convert-csv work with the input filename which starts with a period or an numeric #2339: convert-csv hit Avro naming rules. This should stay in the Avro-backed conversion area, not drive Parquet inspection behavior.

Tangential: #2657 and #2630 show additional CLI coupling to Avro internals, but are mostly binary/API mismatch issues.

Summary

Keep Avro for Avro-facing workflows: schema default output, to-avro, convert, CSV/JSON conversion, and Avro input handling.

Use Parquet-native readers for Parquet inspection and physical rewrites. This preserves the Avro API where intentional while making parquet-cli more robust for valid Parquet files that Avro cannot model.

Appendix

Repro examples

Using parquet-mr version 1.17.1 and fixtures from apache/parquet-testing:

git clone https://github.com/apache/parquet-testing.git
cd parquet-testing

These Parquet inspection commands currently fail:

parquet cat -n 1 data/nested_lists.snappy.parquet
parquet scan data/nested_lists.snappy.parquet

parquet cat -n 1 shredded_variant/case-001.parquet
parquet scan shredded_variant/case-001.parquet

parquet cat -n 1 data/int96_from_spark.parquet
parquet scan data/int96_from_spark.parquet

Observed failure classes:

• data/nested_lists.snappy.parquet: Avro schema conversion succeeds, but cat and scan fail during Avro-backed record reading with ParquetDecodingException, followed by GroupColumnIO.getFirst index failure.
• shredded_variant/case-001.parquet: Avro schema conversion succeeds, but cat and scan fail during Avro-backed record reading with ParquetDecodingException, followed by GroupColumnIO.getLast index failure.
• data/int96_from_spark.parquet: Avro schema conversion fails before reading records with Argument error: INT96 is deprecated..., blocking Parquet row inspection.

[kevinjqliu]

Similar to "Add integration tests for all parquet-testing files" (#3670), might be a good idea to run integration tests for parquet-cli and parquet-testing files