Optimized reads

You can use following query to see how many bytes in your session were optimized:

SELECT name, VALUE
  FROM v$mystat JOIN v$statname USING (statistic#)
 WHERE name IN ('cell flash cache read hits',
                'physical read requests optimized',
                'physical read total IO requests');

You should either reconnect to reset the counter, or run it before/after the query and calculate the differences yourself. 'physical read total IO requests' is how many times a request was sent to the storage (which could be anywhere between 1 and 128 blocks) 'physical read requests optimized' is how many read requests were satisfied by either flash cache or storage indexes 'cell flash cache read hits' is how many read requests were satisfied by flash cache hits

The difference between ‘physical read requests optimized' - 'cell flash cache read hits' is how many requests were satisfied by the storage indexes. This means that the storage index decided that some blocks did not have to be read from the storage because there was no data in it that could satisfy the where clause.

To have similar results in bytes you can use 'physical read total bytes', ‘cell physical IO bytes saved by storage index’ and ‘physical read total bytes optimized’.

SELECT name, VALUE
  FROM v$mystat JOIN v$statname USING (statistic#)
 WHERE name IN ('physical read total bytes',
                'cell physical IO bytes saved by storage index',
                'physical read total bytes optimized');