InnoDB is a transactional storage engine. Two parts of the acronym ACID (atomicity and durability) are guaranteed by write-ahead logging (WAL) implemented by the InnoDB redo log.
A statement within a user transaction can consist of multiple operations, such as inserting a record into an index B-tree. Each low-level operation is encapsulated in a mini-transaction that groups page-level locking and redo logging. For example, if an insert would cause a page to be split, a mini-transaction will lock and modify multiple B-tree pages, splitting the needed pages, and ﬁnally inserting the record.
On mini-transaction commit, the local mini-transaction log will be appended to the global redo log buﬀer, the page locks will be released and the modiﬁed pages will be inserted into the[Read more...]