Re: [PATCH v1] Add and report the new "in_hot_standby" GUC pseudo-variable.

From: pgsql-hackers-owner(at)postgresql(dot)org
> [mailto:pgsql-hackers-owner(at)postgresql(dot)org] On Behalf Of Craig Ringer
> On 13 April 2017 at 14:59, Tsunakawa, Takayuki
> <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> wrote:
>
> > 2. Make transaction_read_only GUC_REPORT This is to avoid the added
> > round-trip by SHOW command. It also benefits client apps that want to
> know when the server gets promoted? And this may simplify the libpq code.
> > I don't understand yet why we need to provide this feature for older servers
> by using SHOW. Those who are already using <= 9.6 in production completed
> the system or application, and their business is running. Why would they
> want to just replace libpq and use this feature?
>
> I think "transaction_read_only" is a bit confusing for something we're
> expecting to change under us.
>
> To me, a "read only" xact is one created with
>
> BEGIN READ ONLY TRANSACTION;
>
> .... which I would not expect to become read/write under me, since I
> explicitly asked for read-only.
>
> It's more like "session read only" that we're interested in IMO.

Are you suggest thating we provide a GUC_REPORT read-only variable "session_read_only" and the libpq should use it?

Anyway, I added this item in the PostgreSQL 10 Open Items page under
"Design Decisions to Recheck Mid-Beta". I'm willing to submit a patch for PG10.

Regards
Takayuki Tsunakawa