On Apr 8, 2004, at 6:33 PM, Josh Berkus wrote:


Mark,

I've got one question about query planning.  Is it understandable to
have the query plan estimation be off by a couple of orders of
magnitude?  Or, is it the fact that the cost estimation is small to
begin with that the error between the actual and the estimated is
"normal"?


Well, your example is not "a couple orders of magnitude". 6 vs. 32 is actually pretty good accuracy.

Now, 6 vs 192 would potentially be a problem, let alone 32 vs 13,471.


I guess I was looking more at the cost estimate and not so much at the rows estimate. I agree that the row estimate wasn't too bad. But the cost estimate seems way out of line.


I'm somewhat new to examining explain analyze output and I'm looking at this as more of an education, since the speed is certainly good anyway. I just expected the cost estimate to be more in line especially immediately after an analyze.

-Mark


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