When records are deleted, they are first delete-marked and finally purged by the InnoDB master thread when the records no longer exist in any active transaction's read view. After the purge, some of the deleted records would be left intact in the free lists of the B-tree index pages. But this garbage will be deleted when InnoDB reorganizes an index page or merges or splits pages to balances the B-tree. Recovering the delete-marked but not purged records is fairly easy, but restoring the purged records is hard. It is good to have backups, not only of the data files, but also the logs.
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