Oracle Database 11g Oracle Real Application Clusters Handbook, 2nd Edition, 2nd Edition

Cache Fusion I or Consistent Read Server

Cache Fusion I (also known as consistent read server) was introduced in version 8.1.5. Oracle keeps a list of recent transactions that have changed a block. The original data contained in the block is preserved in the undo segment, which can be used to provide consistent read versions of the block to other readers or to recover an uncommitted transaction after an instance or a process crash.

Generally, when a transaction is committed, the server process places a flag in the undo segment header indicating the transaction status as “committed.” To save time, it does not stamp each and every block it has modified with a commit flag. Thus, in the future, whenever another process reads that block and finds ...