Lesson 1

In the previous modules, we examined tuning the shared pool and the Oracle data buffer cache. This module discusses Oracle's redo logs and why the redo log is an integral part of the Oracle engine and provides several tuning opportunities that improve Oracle performance. By the time you complete this module, you should be able to:

1. Understand redo log functions
2. Describe the main tuning techniques for the redo log
3. Investigate redo log activity for Oracle tasks
4. Set the redo log parameters
5. Examine redo log wait statistics
6. Determine sizes for online redo logs
7. Set appropriate sizes for the archived redo log file system
8. Change parameters to relieve redo log contention
9. Set log_checkpoint_interval to maximize performance

In the next lesson, we will begin our overview of the redo log.

Question: What are the main tuning techniques for the redo log in Oracle?
Tuning the redo log in Oracle is an essential practice to optimize database performance and ensure data integrity. Proper tuning helps to prevent any potential performance bottleneck. Here are several strategies you can apply for effective tuning:

1. Size the Redo Logs Appropriately: Choose the right size for your redo log files. If the log files are too small, Oracle will have to perform log switches more frequently, causing a performance hit. The alert log file contains information about log switch frequency. Ideally, you should aim for log switches every 15-20 minutes during peak usage. If you observe more frequent log switches, consider increasing the size of your redo logs.
2. Configure Redo Log Buffer: The redo log buffer, part of the System Global Area (SGA), holds information that needs to be written to the redo log files. If your system shows high "redo log space requests," consider increasing the size of the redo log buffer. Use the dynamic performance view V$SYSSTAT to check redo log space requests.
3. Multiplex Redo Log Files: Multiplexing is an approach to enhance the redo log's availability. You can maintain multiple copies of the log files on different disks. If one disk fails, Oracle can access another redo log copy from another disk, ensuring that no data is lost.
4. Use Fast Disk for Redo Logs: For better performance, use faster disks for your redo log files. Placing redo logs on a Solid State Drive (SSD) can help to decrease log file sync wait time significantly.
5. Use Asynchronous I/O: Asynchronous I/O allows for improved performance by allowing the foreground processes to proceed before the writes are completed. If your platform supports asynchronous I/O, enable it for the redo logs.
6. Private Redo Threads: For Real Application Clusters (RAC), private redo threads can improve performance. Private redo threads avoid redo allocation latch contention in high update transaction environments.
7. Avoid Long Running Transactions: Long running transactions require Oracle to keep more redo information in the online redo logs to be able to roll back transactions. This increases "log file sync" waits. Avoiding such transactions can help tune redo log performance.
8. Consider COMMIT Frequency: A higher frequency of COMMIT operations can lead to higher 'log file sync' waits, impacting performance. Design your application to commit less frequently if possible, but ensure that this doesn't compromise the logical transaction integrity.

Remember, each of these techniques may have a different impact on your specific environment, and some may involve trade-offs with other aspects of database performance. Therefore, always perform thorough testing before applying any changes to a production environment. Monitor your system regularly using Automatic Workload Repository (AWR) or Statspack reports to ensure optimal performance of your redo log system.