Re: [HACKERS] make async slave to wait for lsn to be replayed

On Sun, Mar 12, 2017 at 10:20 PM, Thomas Munro
<thomas.munro@enterprisedb.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.