apache / apache/iceberg-python
Enable stats collection for nested fields and use write.metadata.metrics.max-inferred-column-defaults to control stats growth
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- Python
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Description
### Feature Request / Improvement
I recently discovered that full stats collection (i.e. `lower_bounds`/`upper_bounds`) is explicitly [disabled](https://github.com/apache/iceberg-python/blob/7acdb12f5239594e593f2822de75c7a4c669f52f/pyiceberg/io/pyarrow.py#L2220-L2223) in PyIceberg for nested (i.e. struct child) fields.
This change was made in [this PR](https://github.com/apache/iceberg/pull/7831) and specifically [this commit](https://github.com/apache/iceberg/pull/7831/commits/6f7bd987e50d4978aeae333d759e34422f7cfb78).
It seems that this change may have been made to limit the number of fields whose stats are collected when default-full stats collection is enabled. However, after discussion it seems that simply adding support for the `write.metadata.metrics.max-inferred-column-defaults` table [property](https://iceberg.apache.org/docs/nightly/configuration/#write-properties) would be the preferred way to control stats growth. If this is implemented, re-enabling stats collection for nested fields should be a non-issue.
Stats collection for nested struct fields is important for schemas like [GeoParquet](https://geoparquet.org/releases/v1.1.0/) which store important primitive fields (in this case, bounding box xmin, ymin, xmax, ymax) using structs.
See also [this slack thread](https://apache-iceberg.slack.com/archives/C029EE6HQ5D/p1762221916113919) for discussion.
Contributor guide
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Research direction
Start in pyiceberg/io/pyarrow.py around the linked lines that disable statistics for nested fields, then trace how write.metadata.metrics.max-inferred-column-defaults is handled. Done means nested struct fields can collect lower and upper bounds while the table property controls inferred-column statistics growth; use the existing statistics-related tests, if found nearby, to verify both behaviors.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- data-engineering
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Active
- Clarity
- Mostly clear
- Newbie friendliness
- 66/100