advancedxy commented on code in PR #9661:
URL: https://github.com/apache/iceberg/pull/9661#discussion_r1480813301
##########
format/spec.md:
##########
@@ -1117,7 +1117,17 @@ Partition specs are serialized as a JSON object with the
following fields:
|**`spec-id`**|`JSON int`|`0`|
|**`fields`**|`JSON list: [`<br /> `<partition field JSON>,`<br
/> `...`<br />`]`|`[ {`<br /> `"source-id": 4,`<br
/> `"field-id": 1000,`<br /> `"name": "ts_day",`<br
/> `"transform": "day"`<br />`}, {`<br /> `"source-id":
1,`<br /> `"field-id": 1001,`<br /> `"name":
"id_bucket",`<br /> `"transform": "bucket[16]"`<br />`} ]`|
-Each partition field in the fields list is stored as an object. See the table
for more detail:
+Each partition field in the `fields` is stored as a JSON object with the
following properties.
+
+| V1 | V2 | V3 | Field | JSON representation |
Example |
Review Comment:
> it seems the problem existed before then (that V3 is mentioned without a
proper introduction)
Maybe v3 format is not completed and adopted by the community.
How about we introduce `multi-arg` transform in the `### Partitioning` and
`### Sorting` section and point it to the details in the `appendix E`. In the
appendix, we can write detailed documentation about which compatibility flag to
use and how partition field and sort field are json serialized?
Something like this:
```markdown
### Partitioning
... omitted ...
Tables are configured with a **partition spec** that defines how to produce
a tuple of partition values from a record. A partition spec has a list of
fields that consist of:
* A **source column id** or a list of **source column ids** from the
table’s schema
* A **partition field id** that is used to identify a partition field and
is unique within a partition spec. In v2 table metadata, it is unique across
all partition specs.
* A **transform** that is applied to the source column(s)[1] to produce a
partition value
* A **partition name**
... omitted ...
Partition field IDs must be reused if an existing partition spec contains an
equivalent field.
Note:
1. multi-arg transform is added in format Version 3. For details on how
multi-arg transform is serialized in JSON, see appendix E
```
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