Re: Logging WAL when updating hintbit

On Thu, Nov 14, 2013 at 3:02 PM, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com> wrote:
> I attached patch adds new wal_level 'all'.
> If wal_level is set 'all', the server logs WAL not only when wal_level
> is set 'hot_standby' ,but also when updating hint bit.
> That is, we will be able to know all of the changed block number by
> reading the WALs.
Is 'all' a name really suited? It looks too general. I don't have a
name on top of my mind but what about something like full_pages or
something similar...

> This wal_level is infrastructure for fast failback. (i.g., without fresh backup)
> It need to cooperate with pg_rewind.
I am not sure that using as reason the possible interactions of a
contrib module not in core is a reason sufficient to justify the
presence of a new wal_level, and pg_rewind is still a young solution
that needs to be improved. So such a patch looks premature IMO, but
the idea is interesting and might cover many needs for external
projects.

> Not only that, I think it will be profitable infrastructure for
> differential backup.
Yep, agreed. This might help some projects in this area.

> And it leads to improve performance at standby server side. Because
> the standby server doesn't update hintbit by itself, but FPW is
> replicated to standby server and applied.
It would be interesting to see some numbers here.

This is clearly a WIP patch so it does not matter now, but if you
submit it later on, be sure to add some comments in bufmgr.c as well
as documentation for the new option.
Regards,
--
Michael