claudevdm opened a new pull request, #39975:
URL: https://github.com/apache/beam/pull/39975
AddFiles: tighten file schemas with footer null counts, folded per dclared
schema
Parquet writers commonly declare every column optional whatever the data
holds. Taken at face value, a file with no nulls in a column the table has as
required would ask the pre-pass to relax that column for no reason. Tightening
uses the footer's null counts to drop such requests.
The evidence travels beside the schema, not inside it. ReadFooterSchema
emits (canonical declared-schema JSON, proven-null-free paths) and
CollectDistinctSchemas folds the paths per distinct schema by intersection: a
column stays proven only when every file proved it, equivalently a relaxation
is requested when any file needs it. The commit side will rebuild the group's
most conservative member with FileSchemas.markRequired before classifying,
which produces the same table schema as tightening each file individually
would. union adds new columns as optional whatever the file declares.
Tightening only affects columns the table already has as required: the union
adds new columns as optional whatever the file declares.
**Please** add a meaningful description for your change here
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