Support atomic write of large batches of items

[almet]

I was reading a bit some bugzilla and stumbled across this topic, which might be of interest for those of us who want to upload large chunks of data.

https://bugzilla.mozilla.org/show_bug.cgi?id=1250189

I wonder what should be the best approach here. Thoughts?

[leplatrem]

Since the thread on bugzilla is pretty big, I suggest to read this instead : https://github.com/mozilla-services/docs/pull/60/files