rdblue commented on code in PR #16446:
URL: https://github.com/apache/iceberg/pull/16446#discussion_r3284351352
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format/spec.md:
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@@ -514,12 +514,16 @@ Partition field IDs must be reused if an existing
partition spec contains an equ
| **`truncate[W]`** | Value truncated to width `W` (see below)
| `int`, `long`, `decimal`, `string`, `binary`
| Source type |
| **`year`** | Extract a date or timestamp year, as years from 1970
| `date`, `timestamp`, `timestamptz`, `timestamp_ns`, `timestamptz_ns`
| `int` |
| **`month`** | Extract a date or timestamp month, as months from
1970-01-01 | `date`, `timestamp`, `timestamptz`, `timestamp_ns`,
`timestamptz_ns` | `int` |
-| **`day`** | Extract a date or timestamp day, as days from 1970-01-01
| `date`, `timestamp`, `timestamptz`, `timestamp_ns`, `timestamptz_ns`
| `int` |
+| **`day`** | Extract a date or timestamp day, as days from 1970-01-01
| `date`, `timestamp`, `timestamptz`, `timestamp_ns`, `timestamptz_ns`
| `date` [1] |
| **`hour`** | Extract a timestamp hour, as hours from 1970-01-01
00:00:00 | `timestamp`, `timestamptz`, `timestamp_ns`, `timestamptz_ns`
| `int` |
| **`void`** | Always produces `null`
| Any
| Source type or `int` |
All transforms must return `null` for a `null` input value.
+Notes:
+
+1. The result type for `day` has been documented as both `int` and `date` in
earlier revisions of this spec. The physical representation has always been a
4-byte integer counting days from `1970-01-01`, regardless of whether the Avro
field is annotated with `logicalType: date`. Readers may encounter manifests in
either form; per the Avro specification, unrecognized logical type annotations
are ignored, so the bytes on disk are identical.
Review Comment:
I don't agree with the conclusion "so the bytes on disk are identical".
That's true, but not a result of the Avro spec's requirement. How about
"Writers have produced fields with the `logicalType: date` annotation because
Avro requires that readers must ignore unknown logical types. The bytes on disk
are identical so readers must accept both forms and can choose how to pass on
the data."
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