Re: BUG #17928: Standby fails to decode WAL on termination of primary

On Tue, Aug 15, 2023 at 02:36:10PM +1200, Thomas Munro wrote:
> Yeah, I think that sounds quite promising, and funnily enough I was
> just now working on some Perl code that appends controlled junk to the
> WAL in a test like that so we can try to hit all the error paths...

I am pretty sure that adding some junk in a controlled manner is the
only cheap and rather-reliable way to get something..

Not sure if that will help, but what I was playing with some stuff in
the lines of:
-- Store the length up to page boundary.
select setting::int - ((pg_current_wal_insert_lsn() - '0/0') %
setting::int) as boundary from pg_settings where name = 'wal_block_size'
\gset
-- Generate record up to boundary (56 bytes for base size of the record,
-- stop at 12 bytes before the end of the page.
select pg_logical_emit_message(false, '', repeat('a', :boundary - 56 - 12));

Then by injecting some FF's on the last page written and forcing
replay I am able to force some of the error code paths, so I guess
that's what you were basically doing?
--
Michael