Re: Support for N synchronous standby servers - take 2

On Wed, Apr 6, 2016 at 7:03 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>
> On Wed, Apr 6, 2016 at 8:59 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:
> >
> >> BTW, we can move SyncRepUpdateConfig() just after ProcessConfigFile()
> >> from pg_stat_get_wal_senders() and every backends always parse the
value
> >> of s_s_names when the setting is changed.
> >>
> >
> > That sounds appropriate, but not sure what is exact place to call it.
>
> Maybe just after the following ProcessConfigFile().
>
> -----------------------------------------
> /*
> * (6) check for any other interesting events that happened while we
> * slept.
> */
> if (got_SIGHUP)
> {
> got_SIGHUP = false;
> ProcessConfigFile(PGC_SIGHUP);
> }
> -----------------------------------------
>
> If we do the move, we also need to either (1) make postmaster call
> SyncRepUpdateConfig() and pass the parsed result to any forked backends
> via a file like write_nondefault_variables() does for EXEC_BACKEND
> environment, or (2) make a backend call SyncRepUpdateConfig() during
> its initialization phase so that the first call of pg_stat_replication
> can use the parsed result. (1) seems complicated and overkill.
> (2) may add very small overhead into the fork of a backend. It would
> be almost negligible, though. So which logic should we adopt?
>

Won't it be possible to have assign_* function
for synchronous_standby_names as we have for some of the other settings
like assign_XactIsoLevel and then call SyncRepUpdateConfig() in that
function?

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com