The definition in very simple English is ,if all the data being retrieved is present in index, then DB2 satisfy the query without Accessing base table. The index only access in db2 is a key measurement for performance of your SQL Query.
So additional reads of table pages not required,then I/o is reduced, then performance will be increased.
The same you can find in PLAN_TABLE results as
INDEX ONLY: Y
This means Accessing index is enough and no need to access table.
The below five columns you need to refer in PLAN_TABLE
- INDEDEX ONLY