Shulou(Shulou.com)06/01 Report--

Operation mode: Oracle database can run in archive mode and non-archive mode, and can switch between them;

Log file classification: online log file, archive log file;

Online redo log: records the modification of data, can be used for data recovery, log analysis; also called online log file;

LGWR process: writing redo entries in log buffer to redo log file on hard disk;

Important concept: After the user operation is submitted, the data will not be lost;

Log file organization: organized as a group, log groups work in a circular manner. There are at least two log groups in Oracle. When the first log group is full, log switching occurs and logs are written to log group 2. When log group 2 is full, log switching occurs and logs are written to log group 1.

Operation mode: if the database is running in non-archiving mode, online logs will be lost during switching; when the database is running in archiving mode, log files in original log group 1 will be backed up to other directories for archiving when log switching is performed, and these log files are called archive log files; the command archive log list to view the operation mode; the archive path can be manually adjusted, and there can be multiple archive paths to achieve redundancy;

Log file group management: You can add log files to a group; you can also add log groups; different log groups can have different sizes, but the log files in the same group must have the same size; the default size of log groups is 50MB;

Status of log group: 1. CURRENT: Online log file group currently in use 2 ACTIVE: Dirty data in memory associated with log records corresponding to log files in this log group has not been written to data files 3. INACTIVE: Dirty data in memory associated with log records corresponding to log files in this log group is written to data files 4. UNUSED: Not used

Log group switching: automatic or manual;

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