Capacity Planning and Architecture - Expert Oracle RAC Performance Diagnostics and Tuning - page 51

SSKY2 SSKY3 SSKY4

SSKY1

R R7

R5

R1

R3

500:9996

1

R4

R2

2

SCN 9996

Block 450
Block 490

Block 459 Block 550

Block 500

Block 600

SSKYDB

Figure 2-13. Two-way block transfer

The block is found on instance SSKY4 , and the GCS sends the block to instance SSKY3 . 2.

Block Request Involving Three Instances
In scenarios in which the block requested by another instance is not found on the instance that contains the master,
the GCS will request the block to be retrieved from the disk; or if the block is found on another instance, it will send a
message to the holding instance to send a copy of the block to the requesting instance (see Figure 2-14 ).