Support putIfAbsent

[ion-elgreco]

Atomic writes are not possible currently due to this missing put request with a header.

AWS has native support for this now. MinIO, Cloudflare R2 and other S3 APIs also have this, and we can support atomic writes on most S3 APIs, except LakeFS. There is no safe way to write concurrently to a single branch

[arielshaqed]

Hi @ion-elgreco !

Talk about synchronicity, I was just digging into this yesterday... I assume this is for a Delta log-writer? Can I already use Delta with put-if-absent?

Also: does Delta need it for put-object, for complete-multipart-upload, or for both?

[ion-elgreco]

@arielshaqed Yes this for delta-rs (deltalake), see the PR here I did a while ago: delta-io/delta-rs#2813

You can write delta tables with put-if-absent by simply passing this to the storage_options {"conditional_put":"etag"}.

At the moment its just for put-object. We don't leverage multipart-uploads yet