With SmartScans being the most important (and most unique) performance feature for Exadata, it’s incredibly useful to measure how well you’re making use of it.
There are a number of ways you can measure this, but none of these seem to be the DEFINITIVE method to do so. Instead, it’s probably a good idea to more than one formula, if not all, to get a good idea of our SmartScan usage.
Why are there multiple formulas? Because the existing database metrics don’t quite capture what we’re looking to measure. For instance:
- ‘physical read total bytes‘ – is all the data including compressed data AND SmartScan-ineligible data.
- ‘cell physical IO interconnect bytes‘ – includes the writes (multiplied due to ASM mirroring) AND the reads.
- ‘cell IO uncompressed bytes‘ – is the data volume for predicate offloading AFTER the Storage Index filtering and any decompression
- ‘cell physical IO interconnect bytes returned by smart scan‘ – includes uncompressed data.