Re: Parallel scan with SubTransGetTopmostTransaction assert coredump

On Wed, Aug 4, 2021 at 3:21 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
>The idea I sort of had floating around in my mind is a little
>different than what Greg has implemented. I was thinking that we could
>just skip SerializeSnapshot and the corresponding shm_toc_allocate()
>if !IsolationUsesXactSnapshot(). Then on the restore side we could
>just call shm_toc_lookup() with noError = true and skip
>RestoreTransactionSnapshot/RestoreSnapshot if it returns NULL.

I've tried to follow your description and have attached a patch to
hopefully match it, but it doesn't pass "make check-world".
Perhaps I messed something up (apologies if so), or additional changes
are needed to match what you had in mind or correct additional issues
you didn't foresee?

t/001_pgbench_with_server.pl .. 10/?
#   Failed test 'pgbench scale 1 initialization status (got 1 vs expected 0)'
#   at t/001_pgbench_with_server.pl line 108.
...
# creating primary keys...
# pgbench: fatal: query failed: ERROR:  cannot take query snapshot
during a parallel operation
# CONTEXT:  parallel worker
# pgbench: query was: alter table pgbench_accounts add primary key (aid)