Tuning Global Cache - Expert Oracle RAC Performance Diagnostics and Tuning - page 408

Public Interface

Cluster Interconnect

ORADB1 ORADB2 ORADB3 ORADB4

SSKY1 SSKY2 SSKY3 SSKY4

R4

R1

R5

R6

R2 R3

R7

AV7 AV8 AVL9 AV10 AV11 AV12 AV13 AV14 AV15 AV16

GRID_DATA PRD_DATA

Figure 13-10. Resource re-mastering

Instance SSKY1 and instance SSKY2 will continue to master their resources, namely, R1, R2, R3, and R4. As part
of the recovery process, the resources mastered on the failed instance will now have to be mastered by one of the
surviving instances. Oracle uses the lazy remastering concept and hashes the data blocks previously mastered by the
failed instance to one of the surviving instances during recovery. Consequently, per our illustration in Figure 13-9 ,
R6 is inherited by instance SSKY2 and R7 is inherited by instance SSKY3 ; instance SSKY1 is not affected.
At a later time when the user workload has stabilized (recovery is completed, users have failed over, etc.), the
global cache process may revalidate the affinity statistics and perform a remastering operation to place the master on
the instance where the demand is high.
A similar operation happens when a crashed instance joins, or a new instance is added to, the cluster. Basically,
resources are redistributed and removed from each of the available instances and moved to the instance that joined
the cluster.

Monitoring Remastering
One of the primary scalability factors for Oracle is balancing resource demands on each instance by satisfying
requests on local nodes where demand for the resource is high. As discussed earlier, when the number of opens for
the object increases on another instance to number on the current instance, the master moves from the instance
that is currently mastering the instance to the new instance where the demand for the object is higher. This is called
resource remastering for a database object. Affinity is established when most data blocks for a segment are read
into one instance and never ping out. They may be pushed out of the cache and later read back in from disk,