For some reason, I've been under the impression that writing an existing entity is just as expensive, if not more, than writing a new entity, so a lot of my code has focused on ways of breaking entities into smaller entities so that when I modify a property, it incurs less write costs. However, looking now at the documentation, it states that an existing entity put has the following costs:
1 write + 4 writes per modified indexed property value + 2 writes per modified composite index value
Before I go around changing the entire structure of my code, I want to be sure I understand the details. What exactly qualifies an index as "modified"? Say I have 4 indexed string properties and no composite indexes. To put this as a new entity would cost 10 writes (2 + 2(indexed properties)). Say I now modify one of these string properties and put it back. Would that cost 5 writes only (1 + 4 per modified index)? Am I missing anything? Are there any things I should take into consideration?
And what if I had 4 indexed properties and 1 non-indexed property, and I modify only the non-indexed property - this will only cost me 1 write to re-put?