[rossmohax]

Recent S3 consistency improvements are welcome, but S3 still falls behind Google GCS until they support conditional PUTs.

GCS allows object to be replaced conditionally with `x-goog-if-generation-match` header, which sometimes can be quite useful.

[ignoramous]

Vogels spoke briefly about why AWS prefers versioned objects instead here: https://queue.acm.org/detail.cfm?id=3434573

BTW, DynamoDB supports conditional PUTs if your data can fit under 400 KiB.

[CodesInChaos]

How do versioned objects make conditional puts unnecessary? I see little relation between them, except that you could use the version identifier in the condition.

[jjoonathan]

Because they let AWS offload the hard part to you, which is what AWS does best :)

[ryeguy]

This doesn't answer the question being asked.

[skynet-9000]

Why would AWS provide a feature that makes additional transaction and storage charges (as well as subsequent reads to see which is the correct version) irrelevant?

[the_reformation]

S3 (and most AWS services) are extremely price elastic; i.e., the lower you make them cost, the more people use it (a la electricity.) That's why they've done stuff like drop from 50ms billing to 1ms billing, etc.

[ece]

They could still offer it as a client library feature, just tell the users what kind of r/w amplification and guarantees they can expect, and it's something they could optimize later or not.

[CodesInChaos]

You can't reliably implement conditional PUTs in the client, you need a server side mechanism like the `if-match` header.

[ignoramous]

Conditional PUTs aren't possible with versioned objects, but if you desire immutability, then they do help.

To implement serialisation, (as opposed to using Conditional PUTs) one could implement a ledger on top of versioned buckets with LegalHolds: Basically, the object versions part of the main chain are LegalHolded whilst other versions are reconcilled (rebased) onto main and later deleted. Tricky to implement, for sure, compared to say, maintaining a journal in DynamoDB to track PUTs to maintain serial integrity.

[ithkuil]

There is a conditional CopyObject though (x-amz-copy-source-if...)

Can cover some of the use cases

[ryanworl]

Can you explain how this is useful? It seems like the destination is the important thing here not the source.

[ithkuil]

it can be useful for some coordination problems.

for example imagine that you have N writers and you want only the first of them to write something in a n object.

each writer writes their content into "_foo" and each tries to copy that to "foo", with "x-amz-copy-source-if-match". Only one of them will succeed and "foo" will have one consistent value, which all observers (including other writers) can agree who has won.