Re: non-exclusive backup cleanup is mildly broken

At Fri, 13 Dec 2019 18:50:25 -0500, David Steele <david@pgmasters.net> wrote in
> On 12/13/19 3:56 AM, Magnus Hagander wrote:
> > On Fri, Dec 13, 2019 at 9:00 AM Michael Paquier <michael@paquier.xyz I
> > think that's a bad idea to put a restriction of this kind.  There
> >     are large consumers of 2PC, and everybody needs backups.
> > You misunderstood me. I certainly didn't mean that people who use 2PC
> > shouldn't be able to use proper backups -- that would be *terrible*.
> > I meant disallowing pg_start_backup() in a session that had a prepared
> > transaction, and disallowing preparing a transaction in a session with
> > an ongoing backup. They would still work perfectly fine in *other*
> > parallel sessions.
>
> +1.  I think it is reasonable to expect pg_start/stop_backup() to be
> performed in its own session without prepared transactions.
>
> +more if this concession keeps other aspects of the code simpler.

However I don't object to the restriction, couldn't we allow the
cancel_before_shmem_exit to search for the given entry looping over
the before_shmem_exit array? If we don't do that, an assrtion is needed
instead.

Since pg_stop_backup_v2 is the only caller to the function in the
whole server code, making cancel_before_shmem_exit a bit wiser (and
slower) cannot hurt anyone.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center