Why does MySQL need two-phase commit

MySQL Why a two-phase submission is needed

Two stage submission diagram

Why a two-phase submission is needed ？

Guarantee binlog And redolog Data consistency .

If there is no two-stage submission ：

• First write redolog, To write binlog：
  redolog finish writing sth. , I haven't written yet binlog,MySQL Downtime . After the restart ,redolog There are records in it ,MySQL Judge whether the transaction is submitted successfully , but binlog There is no record in the ,binlog And redolog Data inconsistency occurred . because binlog Yes, append write log , In the future binlog This data will always be missing . If used later binlog Recover the data at this point in time , There will be data loss .

• First write binlog, To write redolog：
  binlog finish writing sth. , I haven't written yet redolog,MySQL Downtime . After the restart ,redolog There is no record of ,MySQL Judge transaction commit failure , however binlog There's a record in ,binlog And redolog Data inconsistency occurred . If you use it later binlog Restore data , There is one more transaction operation .