What are the archived redo logs used for?

What are the archived redo logs used for?

Archived redo logs are used to recover a database or update a standby database. Before you restore, you must locate the file. When you locate the files, ensure that the database is in the Open state.

What is online redo log?

The most crucial structure for recovery operations is the online 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 online redo log to protect the database in case of an instance failure.

What is online and offline redo log files in Oracle?

Oracle allows the optional archiving of filled groups of online redo log files, which creates archived (offline) redo logs. A database backup, together with online and archived redo log files, guarantees that all committed transactions can be recovered in the event of an operating system or disk failure.

Why we use redo logs in Oracle?

What Is the Redo Log? 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.

What is Mira in Oracle?

Starting with Oracle Database 12.2, Multi-Instance Redo Apply (MIRA) greatly improves scalability of redo apply for Oracle RAC databases. Instead of merging all threads of redo into a single apply process, multiple apply instances divide the threads of redo between the apply instances.

Why do we need standby redo logs?

If you configure your standby for Maximum Protection, then Standby Redo Logs are required. Because a standby database exists, a second Archiver process (ARC1) will read from a completed Archived Redo Log and transmit the redo over the network to the Remote File Server (RFS) process running for the standby instance.

How redo log files work in Oracle?

Oracle Database assigns each redo log file a new log sequence number every time a log switch occurs and LGWR begins writing to it. When the database archives redo log files, the archived log retains its log sequence number. A redo log file that is cycled back for use is given the next available log sequence number.

What is the definition of online redo log files in a Oracle CDB?

The online redo log files are a critical component in database recovery. In a multitenant container database (CDB), Oracle Enterprise Manager Database Express (EM Express) provides online redo log file information only in the root, not in the pluggable databases (PDBs).

What size should redo log be?

The minimum size permitted for a redo log file is 4 MB. See Also: Your operating system–specific Oracle documentation. The default size of redo log files is operating system dependent.

What’s the difference between archived redo log files?

Oracle Database lets you save filled groups of redo log files to one or more offline destinations, known collectively as the archived redo log.An archived redo log file is a copy of one of the filled members of a redo log group. I hope you have enough minimal understanding with oracle architecture – as based on your question.

What’s the difference between online and offline redo log files?

Oracle Database lets you save filled groups of redo log files to one or more offline destinations, known collectively as the archived redo log.An archived redo log file is a copy of one of the filled members of a redo log group. Online redo Oracle log files are filled with redo records.

How are redo log files identified in Oracle?

Each online or archived redo log file is uniquely identified by its log sequence number. During crash, instance, or media recovery, Oracle properly applies redo log files in ascending order by using the log sequence number of necessary archived and online redo log files.

Which is the active redo log file in lgwr?

The online redo log file that LGWR is actively writing to is called the currentonline redo log file. Online redo log files that are required for instance recovery are called activeonline redo log files. Online redo log files that are not required for instance recovery are called inactive.