MySQL’s undo log

Short Braindump:
– undo log == rollback segment
– everything kept within the tablespace
– primarily for removing data changes that had been written to disk when a crash occurred, but should not have been written, because they were for uncommitted transactions.”
– “History list length 6 is number of unpurged transactions in undo space. It is increased as transactions which have done updates are commited and decreased as purge runs. ” – comes from
– number of undo log entries for a specific transaction can also be found in the TRANSACTION section of INNODB STATUS

1) – “Some Notes About Structures”