On 06/16/2009 03:22 PM, Robert Haas wrote:
> Well, one problem with this is that the actual values are not costs,
> but times, and the estimated values are not times, but costs. The
> planner estimates the cost of operations on an arbitrary scale where
> the cost of a sequential page fetch is 1.0. When we measure actual
> times, they are in milliseconds. There is no point that I can see in
> making it appear that those are the same thing. Observe the current
> output:
Well - the aim was not to make it possible to use the same name for
"<plan-startup-cost>" and "<actual-startup-cost>" but to group them in
some way - so you can decide in some way (prefix or below a distinct
node) if they are related to planning or execution (And thus making it
easier to handle unknown tags).
That <actual-startup-time/> morphed into <startup-cost/> instead of
<startup-time> was just a typo.
Another solution would be to rename <Startup-Cost> into
<Plan-Startup-Cost> for consistency. But grouping them by some node
seems to be a bit more future-proof.
Andres
