On Mon, Jul 13, 2020 at 10:41:28AM +0200, Francisco Olarte wrote: > Rama: > > On Mon, Jul 13, 2020 at 9:52 AM Rama Krishnan <raghuldrag@xxxxxxxxx> 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. You might want to look at this: https://momjian.us/main/presentations/internals.html#mvcc -- Bruce Momjian <bruce@xxxxxxxxxx> https://momjian.us EnterpriseDB https://enterprisedb.com The usefulness of a cup is in its emptiness, Bruce Lee
