[PERFORM] Acceptable level of over-estimation?

[Carlo Stonebanks]

Is there a rule of thumb about when the planner's row estimates are too 
high? In particular, when should I be concerned that planner's estimated 
number of rows estimated for a nested loop is off? By a factor of 10? 100? 
1000?


Carlo 



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Re: [PERFORM] Acceptable level of over-estimation?

[Gregory Stark]

Carlo Stonebanks [EMAIL PROTECTED] writes:

 Is there a rule of thumb about when the planner's row estimates are too high?
 In particular, when should I be concerned that planner's estimated number of
 rows estimated for a nested loop is off? By a factor of 10? 100? 1000?

Not really. It's a big enough difference for the planner to make a bad
decision or it isn't. But if you pressed me I would say a factor of 10 is bad.
A factor of 2 is inevitable in some cases.

-- 
  Gregory Stark
  EnterpriseDB  http://www.enterprisedb.com

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