Re: Fix for visibility check on 14.5 fails on tpcc with high concurrency

On 2022-Nov-23, Peter Geoghegan wrote:

> On Wed, Nov 23, 2022 at 2:54 AM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> > Something like the attached. It would result in output like this:
> > WARNING: new multixact has more than one updating member: 0 2[17378 (keysh), 17381 (nokeyupd)]
> >
> > Then it should be possible to trace (in pg_waldump output) the
> > operations of each of the transactions that have any status in the
> > multixact that includes some form of "upd".
>
> That seems very useful.

Okay, pushed to all branches.

> Separately, I wonder if it would make sense to add additional
> defensive checks to FreezeMultiXactId() for this. There is an
> assertion that should catch the presence of multiple updaters in a
> single Multi when it looks like we have to generate a new Multi to
> carry the XID members forward (typically something we only need to do
> during a VACUUM FREEZE). We could at least make that
> "Assert(!TransactionIdIsValid(update_xid));" line into a defensive
> "can't happen" ereport(). It couldn't hurt, at least -- we already
> have a similar relfrozenxid check nearby, added after the "freeze the
> dead" bug was fixed.

Hmm, agreed. I'll see about that separately.

--
Álvaro Herrera PostgreSQL Developer — https://www.EnterpriseDB.com/
"I'm always right, but sometimes I'm more right than other times."
(Linus Torvalds)