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by ProblemFactory 1299 days ago
Git provides all of those things, as long as everyone agrees on what the current HEAD commit id (hash) is. You could publish that hash in a printed newspaper or with a government regulator. After publishing it is impossible to rewrite commit history without evidence of tampering.

Rewriting history and amending commits forces the recalculation of all commit hashes that follow it, and you end up with a completely different final hash.

AWS QLDB does the same thing with Amazon holding the final hash.
1 comments
inkyoto 1299 days ago
Publishing a commit ID in a printed newspaper does not prevent the data loss nor the tampering with the data.

Destructive operations in a ledger database are simply not available at the API/interface contract level.

A delete operation in a ledger database is non-destructive and does not delete the data but rather creates a new «deleted» revision in the history table. The deleted revision is always available, and it can be «undeleted» as there is nothing special about the deleted revision: it is merely another document revision with the N+1 revision number. The document can be deleted (revision N+1), undeleted (revision N+2), updated multiple times (revision N + M1, N + M2 …), deleted again (revision N + M1 + M2 + P), yet the entire history of all past and current revision(s) is always available, and it can be retrieved/inspected; even after the table is dropped, it can still be undropped without incurring a data loss – all of that is the append-only ledger guarantee.

The only destructive operation that is practically possible is tearing down the entire ledger at the infrastructure level, which is irreversible and will result in a full data loss. However it can be mitigated (to a very large extent) through segregating and locking down access to the infrastructure.

git does not provide the immutability guarantee as it allows destructive operations, therefore it does not qualify for a ledger proper. A commit history can be rewritten or deleted resulting in a data loss. Published commit ID's are of no use if the data has been tampered with later and valuable revisions have been deleted in perpetuity.

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