What is cardinality feedback in Oracle?

What is cardinality feedback in Oracle?

Cardinality feedback was introduced in Oracle Database 11g Release 2 and was renamed Statistics Feedback in Oracle Database 12c. The purpose of this feature is to automatically improve plans for queries that are executed repeatedly, for which the optimizer does not estimate cardinalities in the plan properly.

How do I enable adaptive cursor sharing in 11g?

You use the parameter cursor_sharing=force to enable cursor sharing.

What is Optimizer_adaptive_features?

OPTIMIZER_ADAPTIVE_FEATURES enables or disables all of the adaptive optimizer features, including adaptive plan (adaptive join methods and bitmap pruning), automatic re-optimization, SQL plan directives, and adaptive distribution methods. Oracle Database SQL Tuning Guide for more information about adaptive plans.

What is dynamic sampling Oracle?

Dynamic sampling (DS) was introduced to improve the optimizer’s ability to generate good execution plans. This feature was enhanced and renamed Dynamic Statistics in Oracle Database 12c. It is typically used to compensate for missing or insufficient statistics that would otherwise lead to a very bad plan.

Is bind sensitive Oracle?

A cursor is marked bind sensitive if the optimizer believes the optimal plan may depend on the value of the bind variable. When a cursor is marked bind sensitive, Oracle monitors the behavior of the cursor using different bind values, to determine if a different plan for different bind values is called for.

Is adaptive cursor sharing on by default?

Default behavior cause performance issue.So oracle introduced Adaptive cursor sharing new feature in 11g. Note: 1. From 11g it is enabled by default.

What is Optimizer_index_cost_adj?

OPTIMIZER_INDEX_COST_ADJ lets you tune optimizer behavior for access path selection to be more or less index friendly—that is, to make the optimizer more or less prone to selecting an index access path over a full table scan. For example, a setting of 50 makes the index access path look half as expensive as normal.

What is Optimizer_features_enable in Oracle?

OPTIMIZER_FEATURES_ENABLE acts as an umbrella parameter for enabling a series of optimizer features based on an Oracle release number. For example, if you upgrade your database from release 11.1 to release 12.1, but you want to keep the release 11.1 optimizer behavior, you can do so by setting this parameter to 11.1.

What are the two types of dynamic sampling methods?

Ways Dynamic Sampling Works There are two ways to use dynamic sampling: The OPTIMIZER_DYNAMIC_SAMPLING parameter can be set at the database instance level and can also be overridden at the session level with the ALTER SESSION command. The DYNAMIC_SAMPLING query hint can be added to specific queries.

What is SQL Plan directives?

SQL Plan Directives are one of the functionalities that make up Adaptive Query Optimization in Oracle Database 12c. SQL plan directives are like “extra notes” for the optimizer, to remind it that it previously selected a suboptimal plan, typically because of incorrect cardinality estimates.

How can we stop hard parsing?

Reducing Hard Parsing. The reduction of hard parsing is accomplished by making changes that will increase the number of reusable statements. You can do this by implementing bind variables or modifying instance parameters.

What is CURSOR_SHARING force?

CURSOR_SHARING determines what kind of SQL statements can share the same cursors. Values: FORCE. Forces statements that may differ in some literals, but are otherwise identical, to share a cursor, unless the literals affect the meaning of the statement.