Re: make async slave to wait for lsn to be replayed

On 22 March 2017 at 01:17, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> On Sun, Mar 12, 2017 at 10:20 PM, Thomas Munro
> <thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> > Maybe someone can think of a clever way for an extension to insert a
> > wait for a user-supplied LSN *before* acquiring a snapshot so it can
> > work for the higher levels, or maybe the hooks should go into core
> > PostgreSQL so that the extension can exist as an external project not
> > requiring a patched PostgreSQL installation, or maybe this should be
> > done with new core syntax that extends transaction commands. Do other
> > people have views on this?
>
> IMHO, trying to do this using a function-based interface is a really
> bad idea for exactly the reasons you mention. I don't see why we'd
> resist the idea of core syntax here; transactions are a core part of
> PostgreSQL.
>
> There is, of course, the question of whether making LSNs such a
> user-visible thing is a good idea in the first place, but that's a
> separate question from issue of what syntax for such a thing is best.

(I know this is old, but):

That ship sailed a long time ago unfortunately, they're all over
pg_stat_replication and pg_replication_slots and so on. They're already
routinely used for monitoring replication lag in bytes, waiting for a peer
to catch up, etc.

--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services