DML occurs even if it is not submitted, the SCN is added, and the JOB process will generate SCN, as long as any changes in the database in the database can generate SCN, SCN: System Change Number, Not System Commit Number. That is, the system changes. One point indicator. Not submitted, just because the submission is also one of the changes in the system, it is generally dbwn to modify the data block but not the data file header. Only when the checkpoint occurs, the data file header is updated, that is, only the CKPT process update the data file header (Oracle8, if there is no CKPT process is LGWR update), DBWR only writes only the occurrence of data block checkpoints, followed by checkpoints that do not necessarily contact DBWR write data file, write after the CKPT update control file and data file header When the DBWR write data block finds the log block of the relevant RDBA (location of the log file) of the data block, the log block of the log file is not written yet, the LLGWR must be notified before the DBWR write block writes the log buffer log file. (Ie there is no commit)
