Re: v16dev: TRAP: failed Assert("size > SizeOfXLogRecord"), File: "xlog.c", Line: 1055, PID: 13564

Hi,

On 2023-04-17 13:50:30 -0400, Tom Lane wrote:
> I wrote:
> > Yeah, I just came to the same conclusion.  One thing I don't understand
> > yet: log_newpage_range is old (it looks like this back to v12), and
> > that Assert is older, so why doesn't this reproduce further back?
> > Maybe the state where all the pages are new didn't happen before?
> 
> Bingo: bisecting shows the failure started at
> 
> commit 3d6a98457d8e21d85bed86cfd3e1d1df1b260721
> Author: Andres Freund <andres@anarazel.de>
> Date:   Wed Apr 5 08:19:39 2023 -0700
> 
>     Don't initialize page in {vm,fsm}_extend(), not needed
> 
> So previously, log_newpage_range could only have failed in very
> unlikely circumstances, whereas now it's not hard to hit when
> committing a table creation.  I wonder what other bugs may be
> lurking.

Oh, interesting. We haven't initialized the extra pages added by
RelationAddExtraBlocks() (in <= 15) for quite a while now, so I'm a bit
surprised it causes more issues for the VM / FSM. I guess it's that it's quite
common in real workloads to contend on the extension lock and add extra
blocks, but not in simple single-threaded tests?

Greetings,

Andres Freund