The internal throughput rate for the two tests is shown in Figure 2-7. The ITR numbers show  an improvement of 2.16% with the fast index traversal feature enabled. The improved performance of the RTW workload with fast index traversal enabled is the result  of a reduction in the number of getpage requests against the index buffer pools. In total, eight  indexes were managed by using in-memory structures (FTBs) when  INDEX_MEMORY_CONTROL was set to AUTO. The total average getpage requests per  thread dropped from 289.4 K to 236.8 K (a 18.2% reduction) compared to  INDEX_MEMORY_CONTROL set to DISABLE. Although the fast index traversal feature requires separate (extra) storage to store the  in-memory managed indexes’ root and non-leaf pages, the test results by using the non-data  sharing RTW workload show that setting INDEX_MEMORY_CONTROL to AUTO did not  cause more Db2 real storage usage compared to when the workload was run with  INDEX_MEMORY_CONTROL set to DISABLE. This result occurs because the RTW  workload includes small indexes and all the FTBs only took up less than 1 MB of storage, as  indicated by the  -DISPLAY STATS(IMU)  command output.  Figure 2-7 ITR: Comparing FTB AUTO and DISABLE 36  IBM Db2 12 for z/OS Performance Topics