Oracle Database 12c - Performance Enhancement - Scalable Log Writer

One of the Performance Enhancement in Oracle Database 12c is Scalable Log Writer.

Log writer (LGWR) process and Log Writer Groups (LGnn) Background process are part of the Scalable Log Writer.

Redo Life Cycle 

Life cycle of Redo logs involves processes like Foreground, Redo Buffer, Log writer (LGWR), Redo Log File, System Monitor (SMON) for Instance Recovery and Data Files. 

Redo Generation has multiple buffer strands and each foreground process writes to the respective redo buffer strands. 

Foreground process waits on Log writer (LGWR) to complete a write on large system with multiple CPU and foreground processes for commits. 

New LGWR Behavior

LGWR Process

Newer architecture of Log writer (LGWR) improves by reducing the waits when writing to large or multiple CPU systems.  This is done with the help of concurrent helper process and optimized log file writes. 

However some of the restrictions of Parallel Log writer (LGWR) with standby database are Synchronous redo transport is not supported.  Serial LGWR is used instead.  Asynchronous redo transport is supported. 

Reference / Additional Reading

1. Oracle Documentation

http://docs.oracle.com/cd/B28359_01/server.111/b28318/process.htm

Oracle Database Concepts

11g Release 1 (11.1)

B28318-06

Chapter 9 Process Architecture

2. Oracle Documentation

http://docs.oracle.com/cd/E11882_01/server.112/e41573.pdf

Oracle Database Performance Tuning Guide 11g Release 2 (11.2) E41573-03 

3. Oracle multiple log writer (LGWR) processes

http://www.dba-oracle.com/t_multiple%20log_writer_lgwr_processes.htm