Cry How To...
Rebuild an index
The simplest way to rebuild and index is:
Alter index <index-name> rebuild tablespace <index-tablespace>;
This also has the advantage of not preventing the index from being used whilst it is being rebuilt. The tablespace must be specified otherwise the index will be rebuilt in the current users default tablespace.
Rebuilding the index also allows new storage parameters to be assigned to the index.
If the index is corrupt, it must be dropped and recreated.
- Firstly, identify the original creation parameters:
SELECT COLUMN_NAME FROM USER_IND_COLUMNS WHERE INDEX_NAME = 'index_name';
SELECT TABLE_NAME, UNIQUENESS, TABLESPACE_NAME, INITIAL_EXENT, NEXT_EXTENT, MIN_EXTENTS, MAX_EXTENTS, PCT_INCREASE, PCT_FREE FROM USER_INDEXES WHERE INDEX_NAME = 'index_name';
The above will give you the columns on which the index is based.
- And then drop the index and recreate it:
Drop index <index-name>;
Create [UNIQUE] index <index-name> On <table-name> ( <column-1> [ , <column-n> ] ) tablespace <tablespace> PCTFREE <pct-free> STORAGE ( NEXT <size>K INITIAL <size>K PCTINCREASE <pct_increase> MIN_EXTENTS <min_extents> MAX_EXTENTS <max_extents> );
- In order to reduce the number of extents, when recreating the index
it would be advisable to set the initial extent to the current index
size. The current index size can be found by:
Select sum(bytes) from dba_extents’;
- Alternately see ‘Obtain information about an index’ for a way of determining the exact index size.
- The primary key cannot be dropped or recreated in this way.
This page represents one page of many pages of notes I made whilst working with Oracle 7 through to 10i. I now no longer work with Oracle databases, but hope that these notes will continue to be of benefit to others.
About the author: Brian Cryer is a dedicated software developer and webmaster. For his day job he develops websites and desktop applications as well as providing IT services. He moonlights as a technical author and consultant.