Re: Libpq support to connect to standby server as priority

On Wed, 16 Jan 2019 at 01:02, Tatsuo Ishii <ishii(at)sraoss(dot)co(dot)jp> wrote:

> > From: Tatsuo Ishii [mailto:ishii(at)sraoss(dot)co(dot)jp]
> >> But pg_is_in_recovery() returns true even for a promoting standby. So
> >> you have to wait and retry to send pg_is_in_recovery() until it
> >> finishes the promotion to find out it is now a primary. I am not sure
> >> if backend out to be responsible for this process. If not, libpq would
> >> need to handle it but I doubt it would be possible.
> >
> > Yes, the application needs to retry connection attempts until success.
> That's not different from PgJDBC and other DBMSs.
>
> I don't know what PgJDBC is doing, however I think libpq needs to do
> more than just retrying.
>
> 1) Try to find a node on which pg_is_in_recovery() returns false. If
> found, then we assume that is the primary. We also assume that
> other nodes are standbys. done.
>
> 2) If there's no node on which pg_is_in_recovery() returns false, then
> we need to retry until we find it. To not retry forever, there
> should be a timeout counter parameter.
>
>
IIRC this is essentially what pgJDBC does.

Dave Cramer

davec(at)postgresintl(dot)com
www.postgresintl.com

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