Thursday, 28 January 2016

SQL ordered by Physical Reads (UnOptimized) or (Optimized) ??

Interestingly from 11.2 onwards there is "SQL ordered by Physical Reads (UnOptimized)" Section in AWR Reports and that is for Smart Flash Cache Database, also note Optimized Read Requests are read requests that are satisfied from the Smart Flash Cache ( or the Smart Flash Cache in OracleExadata V2). A very important point is that the concept and use of  'Smart Flash Cache' in Exadata V2 is different from  'Smart Flash Cache' in Database Smart Flash Cache. Also see that the 'Physical Read Reqs' column in the 'SQL ordered by Physical Reads (UnOptimized)' section is the number of I/O requests and not the number of blocks returned. Be careful not to confuse these with the Physical Reads statistics from the AWR section 'SQL ordered by Reads', which counts database blocks read from the disk not actual I/Os (a single I/O operation  may return many blocks from disk).

In this context Optimized reads will be the one which will be served by the smart flash cache

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