Re: [TRAP: FailedAssertion] causing server to crash

On Mon, Aug 07, 2017 at 05:29:34PM +1200, Thomas Munro wrote:
> On Thu, Aug 3, 2017 at 3:03 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > On Fri, Jul 21, 2017 at 1:31 AM, Thomas Munro
> > <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> >> Thanks Neha. It's be best to post the back trace and if possible
> >> print oldestXact and ShmemVariableCache->oldestXid from the stack
> >> frame for TruncateCLOG.
> >>
> >> The failing assertion in TruncateCLOG() has a comment that says
> >> "vac_truncate_clog already advanced oldestXid", but vac_truncate_clog
> >> calls SetTransactionIdLimit() to write ShmemVariableCache->oldestXid
> >> *after* it calls TruncateCLOG(). What am I missing here?
> >
> > This problem was introduced by commit
> > ea42cc18c35381f639d45628d792e790ff39e271, so this should be added to
> > the PostgreSQL 10 open items list. That commit intended to introduce a
> > distinction between (1) the oldest XID that can be safely examined and
> > (2) the oldest XID that can't yet be safely reused. These are the
> > same except when we're in the middle of truncating CLOG: (1) advances
> > before the truncation, and (2) advances afterwards. That's why
> > AdvanceOldestClogXid() happens before truncation proper and
> > SetTransactionIdLimit() happens afterwards, and changing the order
> > would, I think, be quite wrong.
>
> Added to open items.

[Action required within three days. This is a generic notification.]

The above-described topic is currently a PostgreSQL 10 open item. Robert,
since you committed the patch believed to have created it, you own this open
item. If some other commit is more relevant or if this does not belong as a
v10 open item, please let us know. Otherwise, please observe the policy on
open item ownership[1] and send a status update within three calendar days of
this message. Include a date for your subsequent status update. Testers may
discover new open items at any time, and I want to plan to get them all fixed
well in advance of shipping v10. Consequently, I will appreciate your efforts
toward speedy resolution. Thanks.

[1] https://www.postgresql.org/message-id/20170404140717.GA2675809%40tornado.leadboat.com