Re: [patch] demote - Mailing list pgsql-hackers

From Jehan-Guillaume de Rorthais
Subject Re: [patch] demote
Date
Msg-id 20200714231634.7cad6815@firost
Whole thread Raw
In response to Re: [patch] demote  (Andres Freund <andres@anarazel.de>)
List pgsql-hackers
On Tue, 14 Jul 2020 12:49:51 -0700
Andres Freund <andres@anarazel.de> wrote:

> Hi,
> 
> On 2020-07-14 17:26:37 +0530, Amul Sul wrote:
> > On Mon, Jul 13, 2020 at 8:35 PM Jehan-Guillaume de Rorthais
> > <jgdr@dalibo.com> wrote:  
> > >
> > > Hi,
> > >
> > > Another summary + patch + tests.
> > >
> > > This patch supports 2PC. The goal is to keep them safe during
> > > demote/promote actions so they can be committed/rollbacked later on a
> > > primary. See tests. 
> > 
> > Wondering is it necessary to clear prepared transactions from shared memory?
> > Can't simply skip clearing and restoring prepared transactions while
> > demoting?  
> 
> Recovery doesn't use the normal PGXACT/PGPROC mechanisms to store
> transaction state. So I don't think it'd be correct to leave them around
> in their previous state. We'd likely end up with incorrect snapshots
> if a demoted node later gets promoted...

Indeed. I experienced it while debugging. PGXACT/PGPROC/locks need to
be cleared.



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