Server processes write changes to data blocks in the database buffer cache and write redo data into the redo log buffer. The log writer process (LGWR) writes redo log entries sequentially from the redo log buffer to the online redo log. If the database has a multiplexed redo log, then LGWR writes the same redo log entries to all members of a redo log file group.

LGWR handles the operations that are very fast or must be coordinated. It delegates operations that could benefit from concurrent operations to the log writer worker processes (LGnn), which are numbered LG00-LG99. These operations include writing the redo from the log buffer to the redo log file and posting the completed write to the server process that is waiting.

The redo transport worker processes (TTnn), numbered TT00-TTzz, ship redo from the current online and standby redo logs to remote standby destinations that are configured for asynchronous (ASYNC) redo transport.

LGWR can run as a thread or as an operating system process. In addition to database instances, LGWR also runs on Oracle Automatic Storage Management (Oracle ASM) instances. Each database instance in an Oracle Real Application Clusters (Oracle RAC) configuration has its own set of redo log files.