The writeup mentions that concurrent attempts to update a row will be discussed in a future post. The simplified discussion here says that a writer who encounters a write intent of an uncommitted transaction aborts the concurrent transaction.

I believe also that non-repeatable reads would be a potential problem. A transaction could read a row, then read it a second time; if a concurrent, committed transaction mutated the row, the repeated read will return a different result.

I believe that both these problems would be solved by MVCC which I suspect is the next blog post.

But I'm not super great at distributed DB stuff, so please correct me if I've misunderstood!