I've just completed a patch to reduce lock level for CREATE TRIGGER down
to ShareRowExclusiveLock, i.e. blocks writes but not reads.

I'm thinking that it should be possible to add triggers to PostgreSQL
without blocking reads and writes (ShareUpdateExclusiveLock).

There's a couple of ways of doing that, possibly in conjunction with
facilities in Slony.

Is there anybody interested enough to fund that work for inclusion in
9.1?

Thanks,

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Development, 24x7 Support, Training and Services