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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.