Re: Support for N synchronous standby servers - take 2

On Sat, Apr 23, 2016 at 5:20 PM, Michael Paquier <michael.paquier@gmail.com> wrote:
>
> On Sat, Apr 23, 2016 at 7:44 PM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> > On Wed, Apr 20, 2016 at 12:46 PM, Kyotaro HORIGUCHI
> > <horiguchi.kyotaro@lab.ntt.co.jp> wrote:
> >>
> >>
> >> assign_s_s_names causes SEGV when it is called without calling
> >> check_s_s_names. I think that's not the case for this varialbe
> >> because it is unresettable amid a session. It is very uneasy for
> >> me but I don't see a proper means to reset
> >> syncrep_parse_result.
> >>
> >
> > Is it because syncrep_parse_result is not freed after creating a copy of it
> > in assign_synchronous_standby_names()?  If it so, then I think we need to
> > call SyncRepFreeConfig(syncrep_parse_result); in
> > assign_synchronous_standby_names at below place:
> >
> > + /* Copy the parsed config into TopMemoryContext if exists */
> >
> > + if (syncrep_parse_result)
> >
> > + SyncRepConfig = SyncRepCopyConfig(syncrep_parse_result);
> >
> > Could you please explain how to trigger the scenario where you have seen
> > SEGV?
>
> Seeing this discussion moving on, I am wondering if we should not
> discuss those improvements for 9.7.
>

The main point for this improvement is that the handling for guc s_s_names is not similar to what we do for other somewhat similar guc's and which causes in-efficiency in non-hot code path (less used code).  So, we can push this improvement to 9.7, but OTOH we can also consider it as a non-beta blocker issue and see if we can make this code path better in the mean time.