Capacity Planning and Architecture - Expert Oracle RAC Performance Diagnostics and Tuning - page 37

If the usage pattern changes—for example, the number of users on instance SSKY2 increases to 2,000 and on
SSKY1 it drops to 500—the GCS and GES processes, in combination, would evaluate the current usage pattern and
transfer the mastering of the resource via the interconnect to instance SSKY2 . This entire process of re-mastering of
resources is called object affinity . In other words, object affinity is the use of dynamic resource re-mastering to move the
location of the object masters for a database object to the instance where block operations are most frequently occurring .
Object affinity optimizes the system in situations where update transactions are being executed on one instance.
If activity is not localized, the resource ownership is distributed to the instances equitably.
Figure 2-5 illustrates object distribution in a four-node cluster. That is, instances SSKY1 , SSKY2 , SSKY3 , and SSKY4
are mastering resources R1, R2, R3, R4, R5, R6, and R7, respectively.

Public Interface

Cluster Interconnect

ORADB1 ORADB2 ORADB3 ORADB4

SSKY1 SSKY2 SSKY3 SSKY4

R1 R4 R5 R6

R2 R3

R7

AV1 AVL9 AV10 AV11 AV12 AV13 AV14 AV15 AV16 AV17 AV18

GRID_DATA PRD_DATA PRD_FRA

Figure 2-5. Object mastering

Mastering objects on the instance where the user activity is the highest enables optimization across the cluster
and helps achieve workload distribution and quicker startup time. On a busy system, system performance could be
affected if there is a constant change of workload on the instance causing resource utilization to change and in turn
causing frequent re-mastering activity.