In innodb's bufferpool, there are many dirtypage (that is, the data in the memory has been modified but not written back to the file). If you copy the file directly, the data will be lost and the ibdata 1 file will be damaged. When backing up mysql data, you can't directly back up these files, which is the same reason. We must ensure that all data changes in bufferpool are saved to the hard disk file. To do this, we must first stop the write/update/delete operation, and then wait for innodbflushpagestodisk. If we stop writing, we can close the website application or lock the table: