Fetch the rows while minimizing data block touches:
Eliminate sub-optimal large-table full-table scans: Ensure that the fastest access path to the data is chosen.
Use fastest table join method: The optimizer must choose intelligently between nested loop joins, hash joins and star transformation join methods.
Ensure optimal table-joining order: SQL will run fastest when the first table joins deliver the smallest result set.
Choosing optimizer_mode
ALL_ROWS
Minimizes computing resources
For DSS and DW applications
Favors full-table scans (less I/O than indexes)
FIRST_ROWS
Minimizes response time
Favors index access