shard_for_writes() is appropriate, because we're writing. It can happen that the tablet was migrated away and no shard is the owner. In that case the mutation is dropped, as it should be, because "shards" is empty.
shard_for_writes() is appropriate, because we're writing. It can happen that the tablet was migrated away and no shard is the owner. In that case the mutation is dropped, as it should be, because "shards" is empty.