Expert Oracle Exadata - Parent Directory

CHAPTER 7 RESOURCE MANAGEMENTNow let’s run the same load test with instance caging configured for a 75/25 split on the number ofcores assigned to SCRATCH and SNIFF respectively. In this test, SCRATCH gets 12 CPUs (75% of 16 cores), andSNIFF gets 4 CPUs (25% of 16 cores).SYS:SCRATCH> alter system set cpu_count=12;SYS:SNIFF> alter system set cpu_count=4;Figure 7-6 shows the results of our second test. The split isn’t perfect. It is closer to an 80/20 split.Not captured in these tests was the amount of CPU consumed by all the database background processes,so that may account for the some of the difference. It is also important to understand that Oracle’sResource Manager operates in the user space of the O/S process model, rather than the kernel space. Soit cannot directly control the amount of CPU a process consumes inside the kernel; it can only influencethis by throttling processes in the user space. In our summary, we see that the SCRATCH database sessionsconsumed 78.79% of total session CPU, while the SNIFF database used 21.21% of total session CPU. Eventhough the split isn’t perfect, it does show that instance caging made a solid effort to manage thesedatabases to the 75/25 split we defined. Now, this is not to say that instance caging locks the databaseprocesses down on a specific set of physical CPU cores. All CPU cores are still utilized by all databasebackground and foreground processes. Rather, instance caging regulates the amount of CPU time (% ofCPU) a database may use at any given time.Figure 7-6. Test summary: two databases, instance caging, 75% / 25% split203