Can the CBO optimizer be slow ?

Hi,
i have a strange problem with a query. The first time i execute the query it takes 3 or 4 seconds to be executed. The query has a correct plan (i use the FIRST_ROWS hint) and the second time i execute it then the response is quite immediate.
I have tried to use the RULE hint and the plan is the same as with the FIRST_ROWS hint, but the query is very fast the first time too. I've noted that the time the tkproof utility takes to obtain the query plan (with the FIRST_ROWS hint) is similar to the difference between the first and the second execution.
My question is : can the CBO be so slow ?
TIA
Sergio Sette

Neither one of those queries is using the CBO. /* RULE */ and /* FIRST ROWS */ are hints and use th Rules based optimizer.This is what the oracle documentation says :
---8<---
FIRST_ROWS
The optimizer uses a cost-based approach for all SQL statements in the session regardless of the presence of statistics and optimizes with a goal of best
response time (minimum resource use to return the first row of the result set).
--->8---
first_rows (at least with 8.1.6 or later) uses the CBO and can be very slow. I have solved the problem reanalyzing (using the dbms_utility package) all the object in my schema.
Regards
sergio sette

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Can the CBO optimizer be slow ?

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