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Comment by wpietri | Hacker News Reader

Very interesting. The describe it as a rewind. Does anybody know if it's really a rewind, where each log record is reversible? Or do they do the easier thing of saving snapshots and then replaying the log from snapshot to desired point?

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Aurora uses a log-structured storage system, so they just point to a previous version that they haven't garbage collected.

that's correct.

Probably reversible transactions where possible, but with original-state metadata attached to the transaction if it's required to reverse it (https://en.wikipedia.org/wiki/Memento_pattern).

no, we don't perform destructive writes so we are able to simply mark a region of the log as to be skipped. this approach also allows us to move back and forth within the time domain even after a backtrack.

Every thing is recorded.

edit: And I'm being down voted because? Because HN does not enjoy the truth?

The downvotes are probably because the answer wasn't helpful and doesn't mesh with Amazon's statements.

How did that work for everyone deleting their FB account?

How is this conversation helpful to this thread? The question is not "how much does Amazon keep" but "how long/much/granular can I restore".

That sounded like the original question to me. It's an estranged statement to believe otherwise.

So, yes, they save snapshots and take you back to the time of your choosing based off that.

So, yes, they save snapshots and take you back to the time of your choosing based off that.

Okay, but you're most likely wrong with that. If you read about how Aurora works (https://www.allthingsdistributed.com/files/p1041-verbitski.p...) it seems likely that they will be using log entries to rollback database state, rather than retaining "snapshots".

An estranged statement? What does that mean?

How do you know they use the snapshots method, rather than reversing the changes?

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