Re: CBO calculates lower cost, but runs slower...

First:

1. You should understand how CBO works, how different joins work, how CBO calculates costs for different access methods.How different init.ora parameters influence CBO.

then You should know how your data is distributed, what is the growth.

Then u need to decide how much u trust CBO, do u want to just analyze objects and let CBO decide the access path or u give hints to force CBO follow a particular PATH.

In your case i think, the statistics are not upto date, so in first case with whatever statistics are there CBO uses those and finds the best access method, but since data distribution is different, it is taking time. In second case u r forcing CBO to take particular path and join method, which CBO according to statistics prsent thinks is costly but due different data distribution, u get the results fast.

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