Re: subtransaction assert failure

Gavin Sherry <swm@linuxworld.com.au> writes:
> Interestingly, I *cannot* recreate on the single CPU system and I cannot
> get abort() to generate a core.

By that do you mean that you don't see any corefile in the DB directory
when you look after the dust settles?

I ran into the same problem yesterday in another connection, and
eventually realized that the corefile is getting removed because of the
logic I added recently to do WAL replay of CREATE/DROP DATABASE.  The
regression test sequence is short enough (on modern machines) that there
may not be any checkpoint between its start and the point where you have
a crash, so that the initial "CREATE DATABASE regression" operation is
still in the range of WAL entries to be replayed.  In dbcommands.c
it sez:
       /*        * Our theory for replaying a CREATE is to forcibly drop the        * target subdirectory if present,
thenre-copy the source data.        * This may be more work than needed, but it is simple to        * implement.
*/

So what's happening is that WAL replay is wiping the database directory
(including the core file).

I don't really want to change the CREATE DATABASE replay logic, so I was
thinking of suggesting that we hack around this by modifying pg_regress
to force a checkpoint right after its CREATE DATABASE.  Then any crashes
during the regression tests wouldn't cause a replay of the CREATE.  This
is mighty ugly though :-(
        regards, tom lane