Fast Index Rebuild.

An index should be considered for rebuilding under any of the following conditions:

* The percentage of deleted rows exceeds 30% of the total, i.e. if
del_lf_rows / lf_rows > 0.3.
* If the ‘HEIGHT’ is greater than 4.
* If the number of rows in the index (‘LF_ROWS’) is significantly smaller than ‘LF_BLKS’ this can indicate a large number of deletes, indicating that the index should be rebuilt.


Fast Index Rebuild.
The REBUILD option of the ALTER INDEX statement is executed to quickly rebuild an index using the existing index instead of the table:
alter index emp_idx1 rebuild parallel
tablespace user_tblspc1
storage (pctincrease 0);
Index altered.
Any Modifications to the STORAGE clause can be made at this time and the parallel option can also be used if parallelism is enabled in your database.
Using the REBUILD option of the ALTER INDEX statement for quickly rebuilding an index requires the existing index instead of the table. So necessary space should be available to store both the indexes during the REBUILD operation.
You can also REBUILD online clause to allow DML operations on the table. Index Rebuild online is not applicable for Bitmap indexes or for indexes that enfore referential Integirity Constraints.
This code genenates a script to rebuld all the indexes with height greater than 3 for all the users except for SYS user. The script needs to be executed from SYS schema. This can also be executed from individual schemas by minor changes. If you need to exclude indxes of some other users that can also be added/changed in cGetIdx cursor. To execute this code from any schema other than SYS. Execute on DBMS_SQL must be granted from SYS(not system) to the the specified user.

Indexes with height less than three (3) should not be rebuilded. If you want to go for indexes with less heights that can also be customized by changing the height parameter.

Set serveroutput on size 100000
DECLARE
vOwner dba_indexes.owner%TYPE; /* Index Owner */
vIdxName dba_indexes.index_name%TYPE; /* Index Name */
vAnalyze VARCHAR2(100); /* String of Analyze Stmt */
vCursor NUMBER; /* DBMS_SQL cursor */
vNumRows INTEGER; /* DBMS_SQL return rows */
vHeight index_stats.height%TYPE; /* Height of index tree */
vLfRows index_stats.lf_rows%TYPE; /* Index Leaf Rows */
vDLfRows index_stats.del_lf_rows%TYPE; /* Deleted Leaf Rows */
vDLfPerc NUMBER; /* Del lf Percentage */
vMaxHeight NUMBER; /* Max tree height */
vMaxDel NUMBER; /* Max del lf percentage */
CURSOR cGetIdx IS SELECT owner,index_name
FROM dba_indexes WHERE OWNER NOT LIKE 'SYS%';
BEGIN
/* Define maximums. This section can be customized. */
vMaxHeight := 3;
vMaxDel := 20;

/* For every index, validate structure */
OPEN cGetIdx;
LOOP
FETCH cGetIdx INTO vOwner,vIdxName;
EXIT WHEN cGetIdx%NOTFOUND;
/* Open DBMS_SQL cursor */
vCursor := DBMS_SQL.OPEN_CURSOR;
/* Set up dynamic string to validate structure */
vAnalyze := 'ANALYZE INDEX ' || vOwner || '.' || vIdxName || ' VALIDATE STRUCTURE';
DBMS_SQL.PARSE(vCursor,vAnalyze,DBMS_SQL.V7);
vNumRows := DBMS_SQL.EXECUTE(vCursor);
/* Close DBMS_SQL cursor */
DBMS_SQL.CLOSE_CURSOR(vCursor);
/* Does index need rebuilding? */
/* If so, then generate command */
SELECT height,lf_rows,del_lf_rows INTO vHeight,vLfRows,vDLfRows
FROM INDEX_STATS;
IF vDLfRows = 0 THEN /* handle case where div by zero */
vDLfPerc := 0;
ELSE
vDLfPerc := (vDLfRows / vLfRows) * 100;
END IF;
IF (vHeight > vMaxHeight) OR (vDLfPerc > vMaxDel) THEN
DBMS_OUTPUT.PUT_LINE('ALTER INDEX ' || vOwner || '.' || vIdxName || ' REBUILD;');
END IF;

END LOOP;
CLOSE cGetIdx;
END;