[[!comment format=mdwn
 username="joey"
 subject="""re: stable vs unstable keys"""
 date="2018-10-29T18:55:09Z"
 content="""
It's only used to avoid uploading one chunk from one object that the key
points to, and then later upload a chunk from a different object.

While WORM keys could in theory "collide" and the same key point to
different content, that's no different than MD5 or SHA1 keys colliding;
it's a smallish risk, easily quantified, and you take that risk by
choosing to use those keys.

The risk that the content at an url might change varies over time or
something like that, so I think it makes sense to treat URL keys as specially
unstable.
"""]]