[ants_a]

Yes and no. On the primary durability order and visibility order are different. So an async transaction that starts committing later can become visible to readers before a sync transaction that comes before it.

A read-write sync transaction that reads the result of a non-durable transaction cannot commit ahead of the async transaction. But there is no such guarantee for read-only transactions. So a transaction could read a non-durable state, decide that no further action is needed, and have that decision be invalidated by a crash/failover.

To make things even worse, similar things can happen with synchronously replicated transactions. If a committing transaction waiting on replication is cancelled it will become visible immediately. A reasonably written application would run a retry of the transaction, see that the result is there and conclude that no action is necessary, even though the data is not replicated and would be lost if a failover then happens.

[anonymousDan]

Yeah these are the kind of subtle issues I expected the article might be either glossing over or unaware of.