OracleRedolog redo log

In Oracle databases, there is a log file called redo log file, which is commonly known as redolog. There are two types of redolog: Online redo log and archive log.

In Oracle databases, there is a log file called redo log file, which is commonly known as redolog. There are two types of redolog: Online redo log and archive log.

Redo log

In Oracle databases, there is a log file called redo log file, which is commonly known as redolog. There are two types of redolog: Online redo logs and archived logs.

ONLINE Redo log

Online redo log is mainly used for: the Oracle database server suddenly loses power, suddenly restarts, or executes shutdown abort and other commands so that after the server restarts, oracle Database cannot start the instance normally. At this point, online redo logs are useful. Oracle will use online redo logs to restore the database to the time before the server power loss, so that the database can be started normally. In Oracle databases, by default, there are at least two redo log groups, and each group contains at least one redo log file. The log group is not automatically added. After a full log is written, the next log is automatically written. After the next one is fully written, it will start from the first one.

Archive redo log

Archive logs are mainly used for hardware-level errors: the disk's Bad Sectors cause read and write failures, disk damage, and database data loss. Archive log files are used to restore the database to the time point where the archive log is located, and then restore the database to the current time point through online redo log files. Archive log files can be considered as backups of online redo log files. That is, when a redo log file is filled up, the archived log file will keep a copy of its backup. (As mentioned above, online redo log files will be automatically overwritten). Therefore, archiving log files are backups of old online log files.

Oracle 10g REDO log