Honestly I never found the case when this happens, data always falls into 1 shard according to the key. Then comes the concept of shard replica where the shard

Honestly I never found the case when this happens, data always falls into 1 shard according to the key. Then comes the concept of shard replica where the shard can live in several nodes and form a redundancy. However I'm noy sure how usually it's being setup on Postgres