Re: Patch for fail-back without fresh backup

On Fri, Oct 25, 2013 at 8:08 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> On 2013-10-24 13:51:52 -0700, Josh Berkus wrote:
>
> It entirely depends on your workload. If it happens to be something
> like:
> INSERT INTO table (lots_of_data);
> CHECKPOINT;
> SELECT * FROM TABLE;
>
> i.e. there's a checkpoint between loading the data and reading it - not
> exactly all that uncommon - we'll need to log something for every
> page. That can be rather noticeable. Especially as I think it will be
> rather hard to log anything but a real FPI.
>
> I really don't think everyone will want this. I am absolutely not
> against providing an option to log enough information to make pg_rewind
> work, but I think providing a command to do *safe* *planned* failover
> will help in many more.
>

I think it is better providing as option to log enough information
such as new wal_level.
If user doesn't realize until it's too late, such information is
contained in checkpoint record?
For example if checkpoint record contained information of wal_level
then we can inform to user
using by such information.

BTW this information is useful only for pg_rewind?
Is there for anything else?
(Sorry it might has already been discussed..)

Regards,

-------
Sawada Masahiko