TOptimizerMode Enumeration

Specifies the optimizer mode for connection.

Unit

OraClasses

Syntax

TOptimizerMode = (omDefault, omFirstRows1000, omFirstRows100, omFirstRows10, omFirstRows1, omFirstRows, omAllRows, omChoose, omRule);

Values

Value	Meaning
omAllRows	Explicitly chooses the cost-based approach to optimize a statement block with a goal of best throughput (that is minimum total resource consumption).
omChoose	Causes the optimizer to choose between the rule-based and cost-based approaches for a SQL statement. The optimizer selection is based on the presence of statistics for the tables accessed by the statement. If the data dictionary has statistics for at least one of these tables, then the optimizer uses the cost-based approach and optimizes with the goal of the best throughput. If the data dictionary does not have statistics for these tables, then it uses the rule-based approach.
omDefault	Session optimizer mode will not be changed.
omFirstRows	This mode is retained for backward compatibility and plan stability. It optimizes for the best plan to return the first single row.
omFirstRows1	Instruct Oracle to optimize a SQL statement for fast response. It instructs Oracle to choose the plan that returns the first row most efficiently. If you use the version server lower than Oracle 9.0, these values have the same effect as omFirstRows.
omFirstRows10	Instruct Oracle to optimize an SQL statement for fast response. It instructs Oracle to choose the plan that returns the first 10 rows most efficiently. If you use the version server lower than Oracle 9.0, these values have the same effect as omFirstRows.
omFirstRows100	Instruct Oracle to optimize an SQL statement for fast response. It instructs Oracle to choose the plan that returns the first 100 rows most efficiently. If you use the version server lower than Oracle 9.0, these values have the same effect as omFirstRows.
omFirstRows1000	Instruct Oracle to optimize an SQL statement for fast response. It instructs Oracle to choose the plan that returns the first 1000 rows most efficiently. If you use the version server lower than Oracle 9.0, these values have the same effect as omFirstRows.
omRule	Chooses rule-based optimization (RBO). Any other value causes the optimizer to choose cost-based optimization (CBO). The rule-based optimizer is the archaic optimizer mode from the earliest releases of Oracle Database.