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Oracle 8 tuning: Oracle 8 and Expert Systems Technology

Oracle Tips by Burleson Consulting

Oracle 8 and Expert Systems Technology

Rule-Based Optimizer Quiz

Question:

What is true about the rule-based optimizer? (Choose all that apply)

  1. The rule-based optimizer relies on statistics from the ANALYZE command.

  2. The rule-based optimizer chooses indexes based in their selectivity.

  3. The rule-based optimizer requires careful sequencing of items in the FROM and WHERE clause.

  4. The rule-based optimizer is sometimes faster for complex multi-table equi-joins.

Correct Answer:

C, D

Explanation:

The correct answers are C, The rule-based optimizer requires careful sequencing of items in the FROM and WHERE clause, and D, the rule-based optimizer is sometimes faster for complex multi-table equi-joins.  These are two very important points to remember about rule-based optimization.  Question: What is true about the rule-based optimizer? (Choose all that apply)  A is incorrect because only the cost-based optimizer employs statistics.  B is incorrect because the programmer must indicate selectivity by the sequence of items.

Question:

What was listed as a tuning step for rule-based queries?

  1. Ensure that an index exists for the most selective item in the WHERE clause.

  2. Place the table that returns the largest number of rows last in the FROM clause.

  3. Place the Boolean conditions in order from most selective to least selective.

  4. Analyze the table to get the proper statistics for the optimizer.

Correct Answer:

A

Explanation:

The correct answer is A, ensure that an index exists for the most selective item in the WHERE clause.  This is because this determines which index will be invoked.  Question: What was listed as a tuning step for rule-based queries?  B is incorrect because the driving table should be last, not first.  C is incorrect because Booleans should be from least selective to most selective.  D is incorrect because the rule-based optimizer does not use statistics.

Question:

What was listed as a technique for force the use of an index when the rule-based optimizer makes a poor choice? (Choose all that apply)

  1. Invalidate the index by placing a data type mismatch in the WHERE clause

  2. Use and INDEX hint

  3. Re-sequence the Booleans in the WHERE clause to place the desired index column last in the WHERE clause.

  4. Get index statistics with the ANALYZE INDEX command.

Correct Answer:

A, B, C

Explanation:

The correct answer are A, Invalidate the index by placing a data type mismatch in the WHERE clause, B, Use and INDEX hint, and C, Re-sequence the Booleans in the WHERE clause to place the desired index column last in the WHERE clause.  This is because these are all valid ways to force the use of the most selective index.  Question: What was listed as a technique for force the use of an index when the rule-based optimizer makes a poor choice? (Choose all that apply)  D is incorrect because rule-based optimization does not use statistics.

 

If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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