Rama: On Mon, Jul 13, 2020 at 9:52 AM Rama Krishnan <raghuld...@gmail.com> wrote: > I m preparing for interview one of the recruiter asked me mvcc drawbacks as i > told due to mvcc it use more space and need to perform maintenance activity. > Another one is the same data causes an update conflict because two different > transactions can update the same version of the row. > he told its wrong, kindly tell me will you please tell me its correct or > wrong?
I'm not sure I understand your question too well, you may want to refresh/expand. One interpretation is, on a pure MVCC contest, two transactions, say 5 and 6, could try to update a tuple valid for [1,) and end up generating two new tuples, [5,), [6,) and closing the original at either [1,5) or [1,6) . That's why MVCC is just a piece, locking is other. On a MVCC the tuples are locked while a transaction manipulates them. Other transactions may read them, which is why readers do not block writers, but two updates on the same tuple serialize. Francisco Olarte.
