CODEWITHSUNDEEP
amazon-web-servicesamazon-s3eventual-consistency
Alf
Alf

Reputation: 812

What does read-after-write consistency really mean on new object PUT in S3?

Amazon documentation (http://docs.aws.amazon.com/AmazonS3/latest/dev/Introduction.html#ConsistencyModel) states:

"Amazon S3 provides read-after-write consistency for PUTS of new objects in your S3 bucket in all regions with one caveat."

Ignoring the caveat, this means that a client issuing a GET following a PUT for a new object is guaranteed to get the correct result. My question is, would the guarantee also apply if the GET is issued from a different client not the one which did the PUT (assuming of course the GET follows the PUT chronologically)? In other words, is read-after-write consistency simply read-your-write consistency or it works for all clients?

I suspect the answer is that it works globally but can't find a definitive answer.

Upvotes: 32

Views: 24126

Answers (3)

Vic
Vic

Reputation: 71

As of Dec 1, 2020 (https://aws.amazon.com/blogs/aws/amazon-s3-update-strong-read-after-write-consistency/) S3 does provide strong read after write consistency. However, it's still not clear that GET from a different client (other than the client which sent PUT request) will see the updated result. The blog mentions, "What you write is what you will read, and the results of a LIST will be an accurate reflection of what’s in the bucket."

Also in the distributed systems literature there is 'read-your-own-write' consistency model and a 'consistent read across clients after write' is the ultimate objective (not saying that it's impossible).

I suspect that S3 is eventually consistent for reads from different clients. There should be more clarity from AWS on this point, I feel.

Upvotes: 7

John Rotenstein
John Rotenstein

Reputation: 269282

Yes, it would be consistent.

The concept of a 'client' is irrelevant because each API call is independent.

The us-east-1 region (previously known as US-Standard) previously did not have read-after-write consistency, but it is now provided in all regions.

Upvotes: 19

E.J. Brennan
E.J. Brennan

Reputation: 46849

I've always assumed that same you, i.e. that read-after-write applies to all clients, not just the client that did the write.

This blog post seems to confirm it (for what its worth), but I also did not find any definitive answer on official AWS docs:

https://shlomoswidler.com/2009/12/read-after-write-consistency-in-amazon.html

What is Read-After-Write Consistency?

Read-after-write consistency tightens things up a bit, guaranteeing immediate visibility of new data to all clients. With read-after-write consistency, a newly created object or file or table row will immediately be visible, without any delays.

Upvotes: 10

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