Re: Tracking of page changes for backup purposes. PTRACK [POC]

On 12/20/2017 09:29 PM, Pavel Stehule wrote:
>
>
> 2017-12-20 21:18 GMT+01:00 Robert Haas <robertmhaas(at)gmail(dot)com
> <mailto:robertmhaas(at)gmail(dot)com>>:
>
> On Wed, Dec 20, 2017 at 3:15 PM, Pavel Stehule
> <pavel(dot)stehule(at)gmail(dot)com <mailto:pavel(dot)stehule(at)gmail(dot)com>> wrote:
> >> > So I'm somewhat hesitant to proclaim option 5 as the clear winner, here.
> >>
> >> I agree.  I think (4) is better.
> >
> > Can depends on load? For smaller intensive updated databases the 5 can be
> > optimal, for large less updated databases the 4 can be better.
>
> It seems to me that the difference is that (4) tracks which pages have
> changed in the background, and (5) does it in the foreground.  Why
> would we want the latter?
>
>
> Isn't more effective hold this info in Postgres than in backup sw?
> Then any backup sw can use this implementation.
>

I don't think it means it can't be implemented in Postgres, but does it
need to be done in backend?

For example, it might be a command-line tool similar to pg_waldump,
which processes WAL segments and outputs list of modified blocks,
possibly with the matching LSN. Or perhaps something like pg_receivewal,
doing that in streaming mode.

This part of the solution can still be part of PostgreSQL codebase, and
the rest has to be part of backup solution anyway.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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