Re: Patch for fail-back without fresh backup

On Thu, Oct 24, 2013 at 4:22 PM, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com
> wrote:

> .
>>
>
> To fix that, pg_rewind could always start the rewinding process from the
> last checkpoint before the point that the histories diverge, instead of the
> exact point of divergence.

Is that something required even if someone plans to use pg_rewind for a
cluster with checksums enabled ? I mean since only first update after
checkpoint is WAL logged, pg_rewind will break if another update happens
after standby forks. Or would the recovery logic apply first WAL without
looking at the page lsn ? (Sorry, may be I should read the code instead of
asking you)

If we do what you are suggesting, it seems like a single line patch to me.
In XLogSaveBufferForHint(), we probably need to look at this additional GUC
to decide whether or not to backup the block.

That would make the rewinding more expensive as it needs to read through a
> lot more WAL, but I think it would still be OK.

Yeah, probably you are right. Though the amount of additional work could be
significantly higher and some testing might be warranted.

Thanks,
Pavan

--
Pavan Deolasee
http://www.linkedin.com/in/pavandeolasee