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Posted to github@beam.apache.org by GitBox <gi...@apache.org> on 2021/08/24 20:42:49 UTC

[GitHub] [beam] lostluck commented on a change in pull request #15227: Clarify PCollection immutability.

lostluck commented on a change in pull request #15227:
URL: https://github.com/apache/beam/pull/15227#discussion_r695187919



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File path: website/www/site/content/en/documentation/programming-guide.md
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@@ -448,6 +448,12 @@ individual elements. A Beam Transform might process each element of a
 `PCollection` and generate new pipeline data (as a new `PCollection`), *but it
 does not consume or modify the original input collection*.
 
+> **Note:** Beam SDKs avoid unnecessary copying of elements, so `PCollection`
+> contents are logically immutable, not physically immutable. Changes to input
+> elements may be visible to DoFns executing within the same bundle, and may

Review comment:
       Good call.




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