Re: WIP: long transactions on hot standby feedback replica / proof of concept

On Mon, Oct 30, 2017 at 10:16 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Oct 24, 2017 at 1:26 PM, Ivan Kartyshov
> <i(dot)kartyshov(at)postgrespro(dot)ru> wrote:
>> Hello. I made some bugfixes and rewrite the patch.
>
> I don't think it's a good idea to deliberately leave the state of the
> standby different from the state of the master on the theory that it
> won't matter. I feel like that's something that's likely to come back
> to bite us.

I agree with Robert. What happen if we intentionally don't apply the
truncation WAL and switched over? If we insert a tuple on the new
master server to a block that has been truncated on the old master,
the WAL apply on the new standby will fail? I guess there are such
corner cases causing failures of WAL replay after switch-over.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center