Chapter 5 ■ troubleshooting Query transformations
Once we have all this base information about the table and its indexes (note we also have the clustering factor CLUF in this basic information), we can start to determine how to get the information the cheapest way. For example, the CBO will consider a single table access path and from that will consider a Tablescan (cost 3) or index (AllEqRange) (cost 2) and then tell us which was cheapest: Best:: AccessPath: IndexRange. Figure 5-10 illustrates the section in the 10053 that shows this.
Figure 5-11. The optimizer abandons a join because it’s greater than the best so far cost
In the next chapter we’ll cover SQL*Profiles and what to do when an emergency strikes and we need the right performance, fast!