8.2.4 Row permission indexability for correlated subqueries Row permissions improve data security at a lower level of granularity and become an  attractive solution for integrating that security into the database system rather than requiring  application control or implemented by using views. Efficiency of security validation is  paramount; therefore, this enhancement in Db2 12 to resolve indexability of correlated  subquery predicates within a row permission.  Before Db2 12, correlated subquery predicates within a row permission are stage 2  predicates during insert and update operations. A correlated subquery example of a row  permission is highlighted in Figure 8-13. Db2 can now use an index for the EXISTS part of the row permission during insert and  update. Performance results for improved row permission indexability included the IBM Retail Data  Warehouse workload, which featured a modified TPCH queries that used row permissions.  Up to a 99% reduction in CPU and elapsed time was observed. Figure 8-13 Correlated subquery predicates in a row permission Performance results Chapter 8. Query performance  261