In this article we are going to see Oracle Log Writer Background Process.
- Log Writer process (LGWR) is a background Process that writes redo log entries sequentially into redo log file.
- Redo log entries are generated in the redo log buffer of the SGA.
- If the database has a multiplexed redo log, then LGWR writes the same redo log entries to all of the members of a redo log file group
- If oracle database is running in archiving mode then archive log files are created from redo log files. These archive log files are used to in various database recovery techniques.
- Redo log buffer works in circular fashion. It means that it overwrites old entries. But before overwriting, old entries must be copies to redo log files. Usually Log writer process (LGWR) is fast enough to mange these issues. Log writer process (LGWR) writes redo entries after certain amount of time to ensure that free space is available for new redo entries.
- LGWR handles the operations that are very fast,or must be coordinated,and delegates operations to the log writer worker helper processes (LGnn) that could benefit from concurrent operations,primarily writing the redo from log buffer to the redo log file and posting the completed write to the foreground process that is waiting
- Multiple LGnn (Log Writer Worker) processes on multiprocessor systems, The LGWR (Log Writer) creates worker processes (slaves) to improve the performance of writing to the redo log file
- The redo Transport slave process (TT00-zz) ships redo from the current online and standby redo logs to remote standby destinations configured for Asynchronous (ASYNC) redo transport.
Turn off multiple log writers.
The lgwr writes all redo entries that have been copied in the buffer since the last time it wrote when:-
• User commits.
• Three seconds since last write.
• When redo log buffer is 1/3 full or 1MB filled.
• dbwr must write modified dirty buffers
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