MySQL log module of InnoDB engine

Updating the database SQL Statement execution , use redo log and binlog Two log modules .

The process is as follows ：

analyzer -> Permission to check -> actuator -> engine redo log(prepare state ) -> binlog -> redo log(commit state )

Catalog

redo log

binlog

Why do update operations need two log modules ？

Log access order of update operation

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redo log

Redo log .InnoDB Rollback function supported by the engine , It is based on this log .

Changes to the database , That is, add, delete, and modify , It will be recorded in redo log in .

When there is an accident , When the data in the database is wrong , According to redo log Do rollback .

binlog

Archive log . yes MySQL My own journal .

Cannot support transaction rollback , But it can realize data backup .

Why do update operations need two log modules ？

In theory , As far as the update operation itself is concerned , A log module can solve the problem .

But here we see , Two log modules , Different attribution . One is MySQL Self contained , The other is InnoDB Engine implementation .

Log access order of update operation

Notice that the access order of logs in the update operation is like this ：

redo log(prepare state ) -> binlog -> redo log(commit state )

This is to maintain the data consistency of the two logs .

If you write first redo log To write binlog , There is an accident in the middle , The machine stops working . After restart , The machine will according to redo log Restore data , And in the binlog There is no record in the , When it comes to backup , You lose this piece of data .

If you write first binlog , Post write redo log , There is an accident in the middle , Data cannot be recovered , But there are records .

Follow the crossover operation , If it's done redo log(prepare state ) -> binlog There was an accident , You can rely on MySQL Processing mechanism of .

Judge redo log Is it complete , If complete, submit .

redo log No, commit , Go and see binlog Is it complete .

         complete , Then submit redo log Of commit state .

        Incomplete , Roll back .

Okay , That's all for the canto .

Keep early hours , take care . The king of early rising wishes you good luck ！