Checkpoint , Log Writer Archiver Process

The Checkpoint Process

The checkpoint process does three things:

• It signals the database write process (DBWn) at each checkpoint.

• It updates the datafile headers with the checkpoint information.

• It updates the control files with the checkpoint information.

The Log Writer Process

Oracle’s online redo log files record all changes made to the database. logs are written to before the datafiles are. Therefore, it is important to  always protect the online logs against loss by ensuring they are multiplexed. Any changes made to the database are first recorded in the redo log buffer, which is part of the SGA.then Log Writer Process write into logfiles. Log writer write in below conditions

• At each commit

• Every three seconds

• When the redo log buffer is one-third full

After crash a database when restart it  then instance reads the redo log files looking for any committed changes that need to be applied to the datafiles .when we commit, Oracle ensures that what you are committing has first been written to the redo log files before these changes are recorded in the actual datafiles. Commit . does’t mean that you have wriiten into datafiles.If  redo files have lost  then it may possible that your data has been lost  even if you committed it.

Archiver Process

The archiver (ARCn) is an optional background process and is in charge of archiving the filled online redo log files, before they can be overwritten by new data. The archiver background process is used only if you’re running your database in archivelog mode.