Index_Manager

Posted 2021-01-21 jy627625

About Indexes

Oracle Database provides several indexing schemes that provide complementary performance functionality. These are:
1. B-tree indexes: the default and the most common
2. B-tree cluster indexes: defined specifically for cluster
3. Hash cluster indexes: defined specifically for a hash cluster
4. Global and local indexes: relate to partitioned tables and indexes
5. Reverse key indexes: most useful for Oracle Real Application Clusters applications
6. Bitmap indexes: compact; work best for columns with a small set of values
7. Function-based indexes: contain the precomputed value of a function/expression
8. Domain indexes: specific to an application or cartridge.

Guidelines for Managing Indexes

This section discusses guidelines for managing indexes and contains the following topics:

1. Create Indexes After Inserting Table Data

Data is often inserted or loaded into a table using either the SQL*Loader or an import utility. It is more efficient to create an index for a table after inserting or loading the data. If you create one or more indexes before loading data, the database then must update every index as each row is inserted.

Creating an index on a table that already has data requires sort space. Some sort space comes from memory allocated for the index creator. The amount for each user is determined by the initialization parameter SORT_AREA_SIZE. The database also swaps sort information to and from temporary segments that are only allocated during the index creation in the user’s temporary tablespace.

Under certain conditions, data can be loaded into a table with SQL*Loader direct-path load and an index can be created as data is loaded.

Index the Correct Tables and Columns

Use the following guidelines for determining when to create an index: