What is invisible indexes in Oracle 11g?
Oracle 11g introduces a new feature for indexes, invisible indexes, that is useful in several different situations. An invisible index is an index that is maintained by the database but ignored by the optimizer unless explicitly specified. The invisible index is an alternative to dropping or making an index unusable.
How do you make an invisible index visible in Oracle?
Additionally, the invisible indexes can all be made visible by the system modifiable initialization parameter optimizer_use_invisible_indexes. SQL> alter system set optimizer_use_invisible_indexes=true; When an index is made invisible, it is invisible only to the optimizer.
How do you create an invisible index?
Indexes can be created as invisible by using the INVISIBLE keyword, and their visibility can be toggled using the ALTER INDEX command.
Why is Oracle not using my index?
Answer: Oracle SQL not using an index is a common complaint, and it’s often because the optimizer thinks that a full-scan is cheaper than index access. · Wrong optimizer_mode – The first_rows optimizer mode is to minimize response time, and it is more likely to use an index than the default all_rows mode.
Can global temporary table have index?
There is no problem with having an index on a GTT. SQL> SQL> drop table GTT; drop table GTT * ERROR at line 1: ORA-14452: attempt to create, alter or drop an index on temporary table already in use SQL> truncate table GTT; Table truncated.
What is unusable index in Oracle?
Making an Index Unusable When you make an index unusable, it is ignored by the optimizer and is not maintained by DML. When you make one partition of a partitioned index unusable, the other partitions of the index remain valid. You must rebuild or drop and re-create an unusable index or index partition before using it.
How do you check if the index is being used in Oracle?
In Oracle SQL Developer, when you have SQL in the worksheet, there is a button “Explain Plan”, you can also hit F10. After you execute Explain plan, it will show in the bottom view of SQL Developer. There is a column “OBJECT_NAME”, it will tell you what index is being used.
Why index is not being used in SQL?
When an indexed column is wrapped within a function, SQL Server will not use any available index on the column. Since nvarchar has higher precedence than varchar, the AccountNumber column is implicitly converted and the same query plan is produced as in the previous example.
Can we rename index in Oracle?
To rename an index in Oracle SQL, you use the ALTER INDEX command: ALTER INDEX index_name RENAME TO new_index_name; You can replace the index_name with the current name of the index, and the new_index_name with the new name for your index. Your index will now be renamed, assuming you have the correct privileges.
Is a primary key an index?
Yes a primary key is always an index. If you don’t have any other clustered index on the table, then it’s easy: a clustered index makes a table faster, for every operation.
Are there invisible indexes in Oracle 11g Release 1?
Invisible Indexes in Oracle Database 11g Release 1 Oracle 11g allows indexes to be marked as invisible. Invisible indexes are maintained like any other index, but they are ignored by the optimizer unless the OPTIMIZER_USE_INVISIBLE_INDEXES parameter is set to TRUE at the instance or session level.
What is the use of invisible indexes in SQL?
Another potential use for invisible indexes is in situations where specific applications require an index temporarily. An index can be created as invisible to allow specific SQL statements to use the index while leaving the rest of the database unaffected.
Is it possible to turn off the Index in Oracle?
Oracle allows you to turn off the index (make it invisible), yet continue to maintain the index (during any DML—INSERT/UPDATE/DELETE) in case you need to turn it back on quickly. You can do this by making the index visible or invisible:
Is it necessary to use invisible Index in DML?
Since the database must still maintain an invisible index for all DML operations, invisible indexes should not be used unless necessary. Though they should be removed once their purpose has been served, invisible indexes offer substantial advantages for short-term solutions.