Re: Enforcing that all WAL has been replayed after restoring from backup

On Wed, Aug 10, 2011 at 1:19 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Wed, Aug 10, 2011 at 6:53 AM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
>> On Wed, Aug 10, 2011 at 12:44, Heikki Linnakangas
>> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>>> On 10.08.2011 12:29, Magnus Hagander wrote:
>>>>
>>>> On Tue, Aug 9, 2011 at 18:07, Tom Lane<tgl(at)sss(dot)pgh(dot)pa(dot)us>  wrote:
>>>>>
>>>>> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com>  writes:
>>>>>>
>>>>>> On 09.08.2011 18:20, Alvaro Herrera wrote:
>>>>>>>
>>>>>>> How about making the new backup_label field optional?  If absent,
>>>>>>> assume
>>>>>>> current behavior.
>>>>>
>>>>>> That's how I actually did it in the patch. However, the problem wrt.
>>>>>> requiring initdb is not the new field in backup_label, it's the new
>>>>>> field in the control file.
>>>>>
>>>>> Yeah.  I think it's too late to be fooling with pg_control for 9.1.
>>>>> Just fix it in HEAD.
>>>>
>>>> Should we add a note to the documentation of pg_basebackup in 9.1
>>>> telling people to take care about the failure case?
>>>
>>> Something like "Note: if you abort the backup before it's finished, the
>>> backup won't be valid" ? That seems pretty obvious to me, hardly worth
>>> documenting.
>>
>> I meant something more along the line of that it looks ok, but may be corrupted.
>
> Yeah.  I'm frankly pretty nervous about shipping 9.1 with this
> problem, but note that I don't have a better idea.  I'd favor making
> pg_basebackup emit a warning or maybe even remove the backup if it's
> aborted midway through.

I don't understand why we need to change pg_control for this?

Why can't we just add a line to backup_label as the first action of
pg_basebackup and then updated it the last action to show the backup
set is complete?

That would be safe for 9.1

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