Re: [PATCH] Improve EXPLAIN ANALYZE overhead by sampling

On Fri, 2006-05-12 at 12:22 +0200, Martijn van Oosterhout wrote:
> On Thu, May 11, 2006 at 06:37:03PM -0500, Jim C. Nasby wrote:
> > On Tue, May 09, 2006 at 10:37:04PM +0200, Martijn van Oosterhout wrote:
> > > Note that the resulting times still include the overhead actually
> > > incurred, I didn't filter it out. I want the times to remain reflecting
> > > reality as closely as possible.
> >
> > If we actually know the overhead I think it'd be very useful at times to
> > be able to remove it, especially if you're actually trying to compare to
> > the planner estimates. Maybe worth adding an option to the command?
>
> It's not quite as easy as that unfortunatly. Each node can estimate how
> much overhead was incurred on that node. However, each node also
> includes as part of its timing the overhead of all its decendant nodes.
> So to really remove the overhead, the top-level would have to recurse
> through the whole tree to decide what to remove.

Agreed

--
  Simon Riggs
  EnterpriseDB   http://www.enterprisedb.com