Identify index fragmentation

To obtain information about an index:

analyze index <index_name> validate structure;

This populates the table ‘index_stats’. It should be noted that this table contains only one row and therefore only one index can be analysed at a time.

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.

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.