The Optimizer chooses Cost_based approach and optimizes with the goal of best throughput if statistics for atleast one of the tables accessed by the SQL statement exist in the data dictionary. Otherwise the OPTIMIZER chooses RULE_based approach.
What is the function of Optimizer?
The goal of the optimizer is to choose the most efficient way to execute a SQL statement.
What is Execution Plan?
The combinations of the steps the optimizer chooses to execute a statement is called an execution plan.
What are the different approaches used by Optimizer in choosing an execution plan?
Rule-based and Cost-based.
What does ROLLBACK do?
ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction.
What is SAVE POINT?
For long transactions that contain many SQL statements, intermediate markers or savepoints can be declared which can be used to divide a transaction into smaller parts. This allows the option of later rolling back all work performed from the current point in the transaction to a declared savepoint within the transaction.
What are the values that can be specified for OPTIMIZER MODE Parameter?
COST and RULE.
What is COST-based approach to optimization?
Considering available access paths and determining the most efficient execution plan based on statistics in the data dictionary for the tables accessed by the statement and their associated clusters and indexes.
What does COMMIT do?
COMMIT makes permanent the changes resulting from all
SQL statements in the transaction. The changes made by the SQL statements
of a
transaction become visible to other user sessions transactions
that start only after transaction is committed.
What is RULE-based approach to optimization?
Choosing an executing planbased on the access paths available and the ranks of these access paths.
What are the values that can be specified for OPTIMIZER_GOAL parameter of the ALTER SESSION Command?
CHOOSE,ALL_ROWS,FIRST_ROWS and RULE.
