On Thursday, September 27, 2012 6:30 AM Josh Berkus wrote:
> > Yes that is correct. I thought timeline change happens only when
> somebody
> > does PITR.
> > Can you please tell me why we change timeline after promotion,
> because the
> > original
> > Timeline concept was for PITR and I am not able to trace from code
> the
> > reason
> > why on promotion it is required?
>
> The idea behind the timeline switch is to prevent a server from
> subscribing to a master which is actually behind it. For example,
> consider this sequence:
>
> 1. M1->async->S1
> 2. M1 is at xid 2001 and fails.
> 3. S1 did not receive transaction 2001 and is at xid 2000
> 4. S1 is promoted.
> 5. S1 processed an new, different transaction 2001
> 6. M1 is repaired and brought back up
> 7. M1 is subscribed to S1
> 8. M1 is now corrupt.
>
> That's why we need the timeline switch.
Thanks.
I understood this point, but currently in documentation of Timelines, this usecase is not documented (Section 24.3.5).
With Regards,
Amit Kapila.
