Oracle Database - Read Consistency
1 - About
2 - Articles Related
3 - Transaction Tables
The database uses a transaction table, also called an interested transaction list (ITL), to determine if a transaction was uncommitted when the database began modifying the block. The block header of every segment block contains a transaction table.
4 - RAC
Read consistency is guaranteed in single-instance and Oracle Real Application Clusters (Oracle RAC) environments. Oracle RAC uses a cache-to-cache block transfer mechanism known as Cache Fusion to transfer read-consistent images of data blocks from one database instance to another.