[GitHub] [iceberg] emkornfield commented on a change in pull request #4272: Docs: Clarify contract for to file uniqueness

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emkornfield commented on a change in pull request #4272:
URL: https://github.com/apache/iceberg/pull/4272#discussion_r820309464



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File path: docs/common/format/spec.md
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@@ -549,7 +551,10 @@ For example, an `events` table with a timestamp column named `ts` that is partit
 
 Scan predicates are also used to filter data and delete files using column bounds and counts that are stored by field id in manifests. The same filter logic can be used for both data and delete files because both store metrics of the rows either inserted or deleted. If metrics show that a delete file has no rows that match a scan predicate, it may be ignored just as a data file would be ignored [2].
 
-Data files that match the query filter must be read by the scan.
+Data files that match the query filter must be read by the scan. Note that for any snapshot, all file paths
+may appear at most once across all manifest files in the snapshot. If a file path appears more then once, the results of the scan are undefined. Reader implementations may raise an error in this case, but are

Review comment:
       > I'm not sure that I'd consider the result undefined, although I see what you're saying.
   
   I was using undefined behavior in the [PL sense](https://en.wikipedia.org/wiki/Undefined_behavior#:~:text=In%20computer%20programming%2C%20undefined%20behavior,which%20the%20computer%20code%20adheres.).  To be pedantic, I don't think here is statement in the spec yet, about the DELETE being informational only, so that adds to the possibilities, but I didn't list them.




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