Object Affinity and Dynamic Remastering

In addition to dynamic resource reconfiguration, the GCS, which is tightly integrated with the buffer cache, enables the database to automatically adapt and migrate resources in the GRD. This is called dynamic remastering. The basic idea is to master a buffer cache resource on the instance where it is mostly accessed. In order to determine whether dynamic remastering is necessary, the GCS essentially keeps track of the number of GCS requests on a per-instance and per-object basis. This means that if an instance, compared to another, is heavily accessing blocks from the same object, the GCS can take the decision to dynamically migrate all of that object’s resources to the instance that is accessing the object most.

The upper part of the graphic shows you the situation where the same object has master resources spread over different instances. In that case, each time an instance needs to read a block from that object whose master is on the other instance, the reading instance must send a message to the resource’s master to ask permission to use the block.

The lower part of the graphic shows you the situation after dynamic remastering occurred. In this case, blocks from the object have affinity to the reading instance, which no longer needs to send GCS messages across the interconnect to ask for access permissions.

Note: The system automatically moves mastership of undo segment objects to the instance that owns the undo segments.