Re: Proposal: Select ... AS OF Savepoint

On 11/4/07, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>
> On Fri, 2007-11-02 at 13:40 +0100, Hans-Juergen Schoenig wrote:
> > >
> > > I think Simon Riggs is already working on that idea. This one is
> > > fairly easy to implement. I think these are some of the features
> > > only a time-stamp based database can implement. I think database
> > > standards were formed during the time, when the data consistency was
> > > provided with Lock based mechanisms. And moreover i have already
> > > committed on the indexes with snapshot and i am still waiting for
> > > its approval from hackers. If that does go through, then i need to
> > > work on the reverse mapping hash tables, which is really a long
> > > task. So i may not be able to take up time-travel now.
> > >
> >
> >
> >
> >
> > if i remember my last talk with Simon correctly the idea is to have
> > timetravel across transactions.
> > having this feature inside a transaction will not make it into CVS as
> > it is basically of no practical use.
> > i would suggest to put some effort into making it work across
> > transactions. just saving the snapshot is not enough
> > here - there are a couple of other things which have to be taken into
> > consideration (transaction wraparound, etc.)
> >
> >
> > if you want to work on timetravel my team and i can provide some
> > assistance as we wanted to help in this area anyway.

Thanks for your inputs Simon.

Yeh, I'd want to do that for recovery purposes though, not for general
> access.

I guessed it.

The idea was to write a syncpoint every N seconds where we record the
> time and a snapshot of what's in progress.

What exactly is getting recorded here? Will the Syncpoint be similar to the
Undo Log at distinct intervals?
This may be a stupid question. But is it not a good idea to implement
time-travel through the Replication server.

The syncpoints would need to
> be visible in the system like prepared transactions. A superuser could
> reconnect to one of the syncpoints and see data as it was at the
> previous time. Difficulties being dropped objects and the negative
> effects on vacuuming, both of which are surmountable, but are big
> current blockers.
>
> I'm not working on this currently, maybe an 8.5+ feature.
>
> --
> Simon Riggs
> 2ndQuadrant http://www.2ndQuadrant.com
>
>

--
Thanks,
Gokul.
CertoSQL Project,
Allied Solution Group.
(www.alliedgroups.com)