Re: BUG #16129: Segfault in tts_virtual_materialize in logicalreplication worker

On Thu, Nov 21, 2019 at 06:35:55PM +0100, Ondřej Jirman wrote:
> One missing piece is what exactly is the contents of the outstanding output from
> pgoutput plugin, that the replica crashes on and doesn't apply. Are there any
> tools for inspecting the binary output from the pgoutput plugin? Maybe that can
> provide a clue.

So I've looked at it manually, and the segfaulting transaction doesn't make
much sense to me. On primary a row with 37880 byte cover_image was inserted,
but pgoutput plugin sends these records:

B
R - public.videos  title cover_image metadata,...
U - new row where cover_image tuple doesn't have any data, just a flag ('u')
C

Which means 'unchanged toast column' according to logical/proto.c

Yet cover_image is defined as not null.

I guess it's some special handling for VARATT_IS_EXTERNAL_ONDISK.

To me this looks like this transaction is assuming data for bytea column
cover_image are already replicated from earlier?

Maybe it is not though? It's certainly breaking some assumption on the
replica, because this is the precise point where segfault happens.

regards,
    o.

> regards,
>     o.
> 
> > regards
> > 
> > -- 
> > Tomas Vondra                  http://www.2ndQuadrant.com
> > PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services