Hi Michael! > 9 окт. 2017 г., в 17:28, Michael Paquier <michael.paqu...@gmail.com> > написал(а): >> VM is WAL-logged [0] >> FSM is not [1] > > If you are willing to go down this road, here are my takes on the matter: > - Any LSN map should be in a different file than FSM and VM. The VM > uses 2 bits per blocks now, and the FSM 8 bits. The FSM is wanted to > remain small, so trying to plug into it more data is not welcome. The > VM bits also are dedicated to purely visibility matters. We may not > want to use that for the VM. > - Those should not be logged, as we would end up with tracking down > WAL records for things that themselves track the effects of other > records. I was asking about FSM and VM not because I wanted to place something there, but because I was looking for the way to backup FSM and VM efficiently. VM can be copied page-incrementally, FSM cannot.
But the design you are describing resembles PTRACK[0]: fork for page changes tracking, not WAL-logged, but crash safe due to recovery from others WALs. Best regards, Andrey Borodin. [0] https://gist.github.com/stalkerg/ab833d94e2f64df241f1835651e06e4b <https://gist.github.com/stalkerg/ab833d94e2f64df241f1835651e06e4b>
