I'm a newbie and a little confused. On one hand there are posts like this that claim exactly-once delivery and distributed locks are impossible. But on the other hand, if I look at the docs of a distributed database, say Apache Ignite, they will say that they have exactly-once delivery [1] and distributed locks [2]. So ... which is it?
[1] https://ignite.apache.org/docs/latest/key-value-api/continuo...
[2] https://ignite.apache.org/docs/latest/distributed-locks