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
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