This post applies both to non-Exadata and Exadata systems. Before Oracle 11.2 came out, it was true to say that Oracle Parallel Execution slaves always do direct path reads (bypassing buffer cache) when doing full segment scans. This should not be taken simplistically though. Even when you were doing full table scans, then yes the scanning was done with direct path multiblock reads – but if you had to visit other, additional blocks out of the scanning sequence, then these extra IOs were don...
