Re: Parallel scan with SubTransGetTopmostTransaction assert coredump

ср, 4 авг. 2021 г. в 07:41, Greg Nancarrow <gregn4422@gmail.com>:

> 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)
>
> Greg, thanks for the fast response! I suppose that a check
for IsolationUsesXactSnapshot() is also useful in a GetTransactionSnapshot
for the correct processing of a case with NULL transaction snapshot.
This corrects mentioned check-world test.
PFA v7 patch.