Re: On markers of changed data

Hi Michael!
> 9 окт. 2017 г., в 17:28, Michael Paquier <michael(dot)paquier(at)gmail(dot)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>