RussellSpitzer commented on a change in pull request #4301:
URL: https://github.com/apache/iceberg/pull/4301#discussion_r823931461
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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:
@rdblue for the Writer issue. I feel like this is a little ambiguous,
are writers required to use the default value with optional columns or can
different writers behave differently? For me this is a little odd because we
are changing the underlying table schema so I feel like the behavior shouldn't
be implementation dependent.
I think we should say that using the default value for unspecified columns
is the spec behavior, or say that writers should not use the value for any new
values and just use null. I think giving writers the option to choose between
these two behaviors is a bit tricky.
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