The Clustering Factor (CF) is the most important index related statistic, with the efficiency of an index performing multi-row range scans very much dependent on the CF of the index. If the data in the table is relatively well clustered in relation to the index (i.e. it has a “low” CF), then an index range scan can visit relatively few table blocks to obtain the necessary data. If the data is effectively randomised and not well clustered in relation to the index (i.e. has a “high” CF), then an index range scan has to visit many more table blocks and not be as efficient/effective as a result. The CBO will be less inclined to use such an index as a result, depending on the overall selectivity of the query.
Speaking At DOAG 2018 Conference And IT Tage 2018 - I will be speaking at the yearly DOAG conference in December as well as at the IT Tage in November. My talk will be "Oracle Optimizer System Statistics Upd...
Acum 2 zile