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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.

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: 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.