Here there is only one object without a parent, that is A. Thus, this is the root entity of the only entity group that contains A, B, C, D and E. Entity is just a separate entity tree connected by parent-child relationships.
As for the record limit, it applies to the entire group of entities. Therefore, you cannot have more than five updates per second for any of your entities (A, B, C, D, or E), since they all belong to the same group.
You can find more information about avoiding the so-called data warehouse statement (updating objects too often) in this article .
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