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.
(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.
