Support the Parquet ALP encoding in the parquet writer options (format.encoding / datafusion.execution.parquet.encoding) #26936

Is your feature request related to a problem or challenge?

Parquet 2.14.0 added the ALP encoding for FLOAT / DOUBLE columns (see the ALP blog post), and the parquet crate reads and writes it since arrow-rs 60.0.0 (apache/arrow-rs#9372). DataFusion main is on arrow/parquet 60, so it can already read ALP encoded files, but there is no way to write them from SQL or the config:

I want to write to a file like this

COPY (SELECT round(68 + 15 * sin(x / 5000.0) + random(), 2) AS temp_f FROM generate_series(1, 1000000) AS t(x))
TO 'readings_alp.parquet' 
OPTIONS ('format.encoding' 'alp', 'format.dictionary_enabled' 'false');

Note the "alp"

This results in an error:

Error: Invalid or Unsupported Configuration: Unknown or unsupported parquet encoding: alp.
Valid values are: plain, plain_dictionary, rle, bit_packed, delta_binary_packed, delta_length_byte_array,
delta_byte_array, rle_dictionary, and byte_stream_split.

The same happens with SET datafusion.execution.parquet.encoding = 'alp'.

The cause is that DFParquetEncoding in datafusion/common/src/parquet_config.rs has no Alp variant, even though parquet::basic::Encoding::ALP exists and "alp".parse::<Encoding>() works.

Describe the solution you'd like

The command should work and produce ALP encoded files

Describe alternatives you've considered

1. Add an Alp variant to DFParquetEncoding with the FromStr / Display / From<DFParquetEncoding> for parquet::basic::Encoding plumbing, so 'alp' is accepted by datafusion.execution.parquet.encoding and the per-column format.encoding options.
2. Mention it in the config docs (docs/source/user-guide/configs.md) and the parquet writer option docs.
3. Add a sqllogictest that writes a DOUBLE column with 'format.encoding' 'alp' and checks parquet_metadata(...) reports ALP in encodings.

Additional context

• Parquet spec: https://github.com/apache/parquet-format/blob/master/Encodings.md#ALP (parquet-format 2.14.0, "Preview")
• arrow-rs implementation: [Parquet] ALP encoder/decoder support arrow-rs#9372; tracking issue Implement ALP encoding arrow-rs#10541
• Related: BYTE_STREAM_SPLIT was added to DFParquetEncoding the same way.