I was wondering whether someone could verify my understanding regarding the differences between those 3 terms as pertaining to Oracle Databases.
Many sources confuse these terms and do not explain them in detail so it was a bit of a challenge to find info.
From what I gather:
- Commit and fast commit are the exact same thing, all commits are fast commits.
- A fast commit essentially only updates the flag in the transaction table of the undo/rollback segment header to indicate that the transaction has committed. However, the actual block is not revisited meaning that the undo byte address (UBA) in the interested transaction list (ITL) which is located in the header of the data block still points to the transaction table of the corresponding undo segment. Furthermore, the lock bytes of the corresponding rows are not released and the lock count in the ITL is unchanged (rows still locked).
- In a commit cleanout, the block is revisited and the ITL is updated with the commit SCN. However, the lock count in the ITL and the lock byte stored with each row is still not updated (row still locked just like in fast commit), this does not generate redo even though the block is changed.
- Blocks which were committed normally (== fast committed) will undergo Delayed Block Cleanout when they are next touched (and generate redo).
- Blocks which were underwent commit cleanout will undergo Delayed Logging Block Cleanout when they are next touched (and generate redo).
Hopefully someone can verify these points! Thanks!