When you say that there can't be sharding without more than one one node taking writes, I totally see where you're coming from. And I agree with you. Typically

When you say that there can't be sharding without more than one one node taking writes, I totally see where you're coming from. And I agree with you. Typically that means that there is a logical isolation between which data goes to which shard so this avoids conflicts too. Usually when people talk about "multimaster" I do not believe they're thinking of this particular scenario but I may be wrong. I'm not familiar but does postgres not shard?