[ncruces]

You can?

You create a multi-part with 3 chunks: the 1st part is a copy range of the prefix, the 2nd part the bit you want to change, and the 3rd a copy range of the suffix?

And yes, all of this is useless for heavy (and esp. concurrent) writes.

[rad_gruchalski]

We both said the same thing. You kinda can but cannot. Yes, you can replace some part of an existing object but you cannot resize it, not can you do anything parallel with that. So you kina can but cannot. And this trick will work in gcs and azure, here you have to move the new object to an old key yourself after the roll up. But why not while you’re already at it.

[ncruces]

You can do it “in place” as the target can be the same as the source. And you can definitely resize it, both truncate it and extend it. The only restriction, really, is that all parts except for the last one need to be at least 5MiB.

GCS compose can also have target be one of the source objects, so you can append (and/or prepend) “in place.”

For GCS compose the suffix/prefix need to be separate visible objects (though you can put a lifecycle on them). For multipart, the parts are not really objects ever.

The performance isn't great because because updating the “index” is slow and rate limited, not because the APIs aren't there.