Re: [COMMITTERS] pgsql: Add a hook in ExecCheckRTPerms().

On Fri, 2010-07-09 at 13:21 -0400, Tom Lane wrote:
> > Agreed that permission checks should logically be applied at
> execution
> > time. I am proposing a performance optimisation, not a change in
> > behaviour.
> 
> Except that it *is* a change in behavior: the first check will occur
> too
> soon.

Sooner matters why? We already have a lock on the table at plan time so
there cannot be a concurrent GRANT against a plan-then-execute
transaction. Later transactions would invalidate and replan.

> The fact that we're interested in adding plugin permissions checking
> pretty much destroys the idea anyway.  You cannot assume that a plan
> cache invalidation will happen for any change in external state that
> a plugin might be consulting.

Plugin can still be executed at appropriate time, its mostly absent and
so cheap. I guess we can keep plugin whatever else I attempt.

> > The proposed performance enhancement would be very useful since we
> have
> > to check permissions of functions, views, tables and every other
> aspect.
> > We could spend a while quantifying that overhead, though "non-zero"
> is
> > all we need to know.
> 
> No, it's not all we need to know.  If you can't prove the overhead
> involved here is significant, we should not be expending effort and
> creating subtle behavioral changes in pursuit of a minor optimization.

OK, will gather evidence.

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