undo log
A logging mechanism in InnoDB used for transaction rollback and multi-version reads. It records the old values of data before modification, forming a version chain that supports MVCC snapshot reads.
Timeline (last 90 days)
The undo log works well for reversible operations (such as moving and renaming files), but it cannot do anything about irreversible actions such as emails and messages already sent out.
InnoDB's write path is log-first: any modification is first written to the redo log, then dirty pages are flushed asynchronously; after a crash, recovery is done by replaying redo, and rollback and multi-version reads are achieved through undo.
Atomicity in the ACID properties of database transactions is implemented through Write-Ahead Logging (WAL) and undo log mechanisms.
All Facts (3)
The undo log works well for reversible operations (such as moving and renaming files), but it cannot do anything about irreversible actions such as emails and messages already sent out.
50%UnverifiedInnoDB's write path is log-first: any modification is first written to the redo log, then dirty pages are flushed asynchronously; after a crash, recovery is done by replaying redo, and rollback and multi-version reads are achieved through undo.
50%UnverifiedAtomicity in the ACID properties of database transactions is implemented through Write-Ahead Logging (WAL) and undo log mechanisms.
50%