Re: Problem with PITR recovery

On Tue, 19 Apr 2005, Simon Riggs wrote:

> On Tue, 2005-04-19 at 08:55 +0400, Oleg Bartunov wrote:
>> On Mon, 18 Apr 2005, Simon Riggs wrote:
>>> but I'm not sure it's best practice to delete them at that point. I
>>> would recommend that users keep at least the last 3 backups. So, I'd
>>> prefer the wording
>>>
>>> ...all archived WAL segments with names numerically less will no longer
>>> be needed as part of that backup set. You may delete them at that point,
>>> though you should consider keeping more than one backup set to be
>>> absolutely certain that you are can recover your data.
>>
>> I see that clear and deterministic procedure of online backup as I imagined
>> earlier becomes fuzzy and blurred :)
>
> The process is involved and requires strictly observed administration
> procedures, just as it does with other database systems. Each of them
> have difficulties that need to be surmounted and require much thought to
> implement. If PostgreSQL is the first DBMS on which you have attempted
> to implement transactional archive recovery then you will definitely
> find it hard, just as most Oracle and SQLServer DBAs don't understand
> how their log recovery systems work either.

This is not an argument ! It's shame we still don't understand do we really
have reliable online backup or just hype with a lot of restriction and
caution. I'm not experienced Oracle DBA but I don't want to be a blind user.
I read seminal papers about recovery and I thought I understand how
it should works in our system. I want to be 110% sure to claim we're
ready to recommend it to our clients. I'm sure there are many experienced
DBA's who also don't understand what we have right now, especially after
this thread.

>
>> This is obviously not suited even
>> for my notebook.
>
> Thats a pretty silly comment Oleg.
>

Don't be silly, Simon. It was just my reaction !

> Since most laptops require portability as the main objective and that
> usually requires or at least must frequently expect disconnection from
> networks and other peripheral devices such as tape units, then no, the
> PITR design isn't suitable in general for laptop use. If you use your
> notebook as a production system with online archiving then PITR is
> suitable.
>
> PITR was designed to offer data protection for major production systems.
> My experience was that these sites would have a reasonable stream of
> transactions coming through, making the time between log file switches
> somewhat predictable and usually every few minutes. The use case of a
> very low transaction rate system was not considered fully since it was
> felt that people in that situation would be less bothered to protect
> their data with a rigorous backup procedure, leaving the issue we have
> been discussing.
>
> If you want recoverability, use PITR. If you choose not to use PITR,
> thats fine. If you'd like to help make it better, that's fine too.
>

These sentences are not fair, Simon. I understand your point but I want
to have postgresql applicable not just for major production systems.
You forget that before production stage you have a lot of development and
testing. I don't want something exotical and I'm a bit surprized
about your reaction. I don't want to think about how difficult backup in
Oracle and other major dbms you're so experienced ! I'm PostgreSQL user
and PostgreSQL is rather transparent system and I'd like to have
understandable recovery process. Now I see all limitations and cautions and
waiting for improvements. Nobody attack you, I'm a bit dissapointed, but
this is what we have.

> Best Regards, Simon Riggs
>
>

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83