rdblue commented on a change in pull request #4301:
URL: https://github.com/apache/iceberg/pull/4301#discussion_r823224333
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File path: format/spec.md
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@@ -193,10 +193,38 @@ Notes:
For details on how to serialize a schema to JSON, see Appendix C.
+#### Default value
+Default values can be assigned to top-level columns or nested fields. Default
values are used during schema evolution when adding a new column. The default
value is used to read rows belonging to the files that lack the column or
nested field prior to the schema evolution.
Review comment:
> I would skip "New" here. I think default values are not used on the
write path at all.
New is doing some useful work. Streaming engines tend to plan writes once
and keep running them. And it's okay to do that. If Flink is writing with
schema id=2 that is missing a column that was added in schema id=3, it can
continue doing that.
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