[MySQL learning notes 32] mvcc

redo log Redo log

redo log It records the physical modification of the data page when the transaction is committed , It is used to achieve the persistence of transactions
The log is divided into two parts ： Redo log buffer and redo log file , The former is in memory , The latter is on disk . After the transaction is committed, all modification information will be saved to the log file , Used to refresh dirty pages （ That is, uncommitted data ） Restore data usage when disk errors occur .

undo log Rollback log

MVCC

Implicit fields

Field name	meaning
DB_TRX_ID	Recently modified transactions ID, Record the transaction that inserted this record or last modified it ID
DR_ROLL_PTR	rollback pointer , Record the last version of this record , Used for coordination undo log, Point to the previous version
DB_ROW_ID	Hide primary key , If the table structure does not specify a primary key , Hidden primary keys will be automatically generated

Version chain

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