LGWR or Redo Log writer or Log writer processback,”The log writer process (LGWR) is responsible for redo log buffer management–writing the redo log buffer to a redo log file on disk. LGWR writes all redo entries that have been copied into the buffer since the last time it wrote.The redo log buffer is a circular buffer. When LGWR writes redo entries from the redo log buffer to a redo log file, server processes can then copy new entries over the entries in the redo log buffer that have been written to disk. LGWR normally writes fast enough to ensure that space is always available in the buffer for new entries

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ARC 0..t or Redo Log Archiveback,”Writes filled redo logs to the archive log destination(s). It is known as the archiver, The archiver process (ARCn) copies online redo log files to a designated storage device after a log switch has occurred. ARCn processes are present only when the database is in ARCHIVELOG mode, and automatic archiving is enabled.An Oracle instance can have up to 10 ARCn processes (ARC0 to ARC9). The LGWR process starts a new ARCn process whenever the current number of ARCn processes is insufficient to handle the workload. The alert file keeps a record of when LGWR starts a new ARCn process.If you anticipate a heavy workload for archiving, such as during bulk loading of data, you can specify multiple archiver processes with the initialization parameter LOG_ARCHIVE_MAX_PROCESSES. The ALTER SYSTEM statement can change the value of this parameter dynamically to increase or decrease the number of ARCn processes. However, you do not need to change this parameter from its default value of 1, because the system determines how many ARCn processes are needed

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