What is the Difference Between Online Redo Logs and Standby Redo Logs

The main difference between online redo logs and standby redo logs is that online redo logs are a set of online redo log files in which each redo log consists of a set of redo entries while standby redo logs are a set of redo log files that are located on the standby database site.

Generally, RDBMS is a DBMS that is designed according to the relational model. Oracle RDBMS is a product of Oracle Corporation. Many organizations use Oracle RDBMS to store and manage their data. Also, it provides facilities such as data security, scalability, improvement in performance, easiness to analyze and manage data, etc. Redo log is a set of files in a proprietary format which contains all changes made to a database. Overall, online redo logs and standby redo logs are two concepts related to this database.

Key Areas Covered

1. What are Online Redo Logs
     -Definition, Functionality
2. What are Standby Redo Logs
     -Definition, Functionality
3. Difference Between Online Redo Logs and Standby Redo Logs
     -Comparison of key differences

Key Terms

Online Redo Logs, RDBMS, Redo, Standby Redo Logs

Difference Between Online Redo Logs and Standby Redo Logs - Comparison Summary

What is Online Redo Logs

Generally, an Oracle database has two or more online redo log files. A collection of online redo log files is called a redo log for the database. Furthermore, a redo log is a collection of record entries or redo records. Difference Between Online Redo Logs and Standby Redo Logs

The online redo log is capable of storing the copy of changes made to data. For example, assume a situation of database failure. In that case, a data file is restored from the backup. It is possible to obtain the recent data changes that are not available in the restored file from the online redo log files. Therefore, the data is always available.

Online redo log files can be used during hardware, software or media failures to recover the database. Moreover, it is possible to multiplex the online redo log files. It helps to store two or identical copies of the online redo log files in various disks. Additionally, an online redo log has a group of online redo log files. There is an online redo log file and multiplexed copies in one group. Every identical copy is a member of the group.

What is Standby Redo Logs

Users can configure Oracle to get maximum performance. However, even though the users are in the max performance, it is useful to implement standby redo logs. Here, a standby redo log is in the standby database site. Further, the standby redo file is similar to an online redo file. However, a standby redo log helps to store data that was received from a primary database.

Oracle data guard has issues with losing last redo log. If the primary instance crashes, it is necessary to flush the current redo log. That should occur before applying the most recent changes applied to the standby database. Not flushing the current redo can cause a data loss forever.

Difference Between Online Redo Logs and Standby Redo Logs

Definition

Online redo logs are a collection of online redo log files of a database in which every redo log consist of redo entries. In contrast, standby redo logs are a collection of redo log files that are residing on the standby database site.

Usage

Furthermore, online redo log files can be used during hardware, software or media failures to recover the database. On the other hand, standby redo logs help to store redo data that has been received from a primary database.

Conclusion

In brief, redo logs are a set of files in a proprietary format which contains the history of all modifications made to a database. There are two types of redo logs in Oracle: online redo logs and standby redo logs. The main difference between online redo logs and standby redo logs is that online redo logs are a set of online redo log files in which each redo log consists of a set of redo entries while standby redo logs are a set of redo log files that are located on the standby database site.

References:

1.“Standby Redo Logs – Why and How?” Standby Redo Logs Why and How Version History, Available here.
2.“Redo Log.” Wikipedia, Wikimedia Foundation, 13 Aug. 2017, Available here.
3.“Standby Redo Log Files Tips.” Oracle Standby Redo Log Recovery, Available here.
4.“Database 2 Day DBA.” About Online Redo Log Files, 17 Jan. 2017, Available here.

Image Courtesy:

1.”database” By RRZEicons – Own work (CC BY-SA 3.0) via Commons Wikimedia

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