Redo log for each database instance referred as redo thread - Oracle Redo Log

Q.  What does the redo log for each database instance referred to as in the context of multiple database instances?
- Published on 04 Aug 15

a. Redo thread
b. Redo entry
c. Redo record
d. All mentioned above

ANSWER: Redo thread


  • Nirja Shah   -Posted on 24 Sep 15
    - The most crucial structure for recovery operations is the redo log, which consists of two or more preallocated files that store all changes made to the database as they occur.

    - Every instance of an Oracle Database has an associated redo log to protect the database in case of an instance failure.

    - Redo Threads - When speaking in the context of multiple database instances, the redo log for each database instance is also referred to as a redo thread.
    - In typical configurations, only one database instance accesses an Oracle Database, so only one thread is present.
    - In an Oracle Real Application Clusters environment, however, two or more instances concurrently access a single database and each instance has its own thread of redo.
    - A separate redo thread for each instance avoids contention for a single set of redo log files, thereby eliminating a potential performance bottleneck.

    - Redo log files are filled with redo records.

    - A redo record, also called a redo entry, is made up of a group of change vectors, each of which is a description of a change made to a single block in the database.

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