Re: On markers of changed data

On Mon, Oct 9, 2017 at 2:23 PM, Andrey Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>> I haven't gone and audited it myself, but I would certainly expect you
>> to be able to use the LSN for everything which is WAL'd. If you have
>> cases where that's not the case, it'd be useful to see them.
>
> Thanks, Stephen, this actually pointed what to look for
> 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.
--
Michael