by-nc-sa     개발자, DBA가 함께 만들어가는 구루비 지식창고!

3.1 Undo Segment란?




Undo 가 하는 일

1. Rollback an active transaction

2. Recover a terminated transaction

3. Provide read consistency [ Undo_Retention ]

MCVV(Multi-Version Concurrency Control )

# QUERY SCN >= BLOCK SCN ==> 그냥 Read
# QUERY SCN < BLOCK SCN ==> CR Operation 수행 ( UNDO Base 로 )

4. Recovery From Logical Corruption (=Flashback ) [ Undo_Retention ]

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