How recover database if redo log is corrupted?

How recover database if redo log is corrupted?

Recovering After the Loss of All Members of an Online Redo Log Group

1. Locate the filename of the lost redo log in V$LOGFILE and then look for the group number corresponding to it.
2. Determine which groups are active.
3. If the affected group is inactive, follow the procedure in Losing an Inactive Online Redo Log Group.

What is the use of redo log files in Oracle?

Redo log files are operating system files used by Oracle to maintain logs of all transactions performed against the database. The primary purpose of these log files is to allow Oracle to recover changes made to the database in the case of a failure.

How does Oracle protect redo from being overwritten?

Verifying Blocks in Redo Log Files Oracle Database uses the checksum to detect corruption in a redo log block. The database verifies the redo log block when the block is read from an archived log during recovery and when it writes the block to an archive log file.

How do I recover data from a redo log file?

To recover from loss of an active online redo log group in ARCHIVELOG mode:

1. Begin incomplete media recovery.
2. Ensure that the current name of the lost redo log can be used for a newly created file.
3. Open the database using the RESETLOGS option:

What will happen if redo log file was corrupted?

A redo log file might become corrupted while the database is open, and ultimately stop database activity because archiving cannot continue. In this situation the ALTER DATABASE CLEAR LOGFILE statement can be used to reinitialize the file without shutting down the database.

Can we drop active redo log group?

You can drop a redo log member only if it is not part of an active or current group. If you want to drop a member of an active group, first force a log switch to occur. Make sure the group to which a redo log member belongs is archived (if archiving is enabled) before dropping the member.

What is difference between archive and redo log?

Archive logs are archived redo(online) log files. In redo log files are all changes that happened to your data. If your database is in archivelog mode, than redo logs can’t be overwritten, they are archived in some other location when they are full. Redo and archive logs are used in various database recovery scenarios.

What does redo log file contain?

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.

Can we delete redo log files?

It is permissible to drop redo log files so that a multiplexed redo log becomes temporarily asymmetric. For example, if you use duplexed groups of redo log files, you can drop one member of one group, even though all other groups have two members each.

What is the difference between redo log and archive log?

How do you calculate redo log?

I discovered that I have 15 groups of 2 GB, so the redo log group size is 30 GB. Oracle says that “In general we recommend adding an additional 30% on top of the peak rate”, so that would mean I am expected to have 245mb/s*1.3 = 318.5 MB/S.

How do I find my archive log list?

Answer: The archived redo logs will be in the flash recovery area in the ARCHIVELOG directory….The following commands can be used to locate the Oracle archive logs:

1. Issue the archive log list command: SQL> archive log list.
2. Issue the show parameter command:
3. Query the v$archive_dest view:

How does redo log work in Oracle Database?

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.

How to recover from the loss of redo log files?

Now it depends on the a.status and a.archived column of the above query, to decide how to proceed with the recovery.

When does lgwr overwrite a redo log file?

If archiving is disabled (the database is in NOARCHIVELOG mode), then when the last redo log file is full, LGWR continues by overwriting the next log file in the sequence when it becomes inactive. A log switch is the point at which the database stops writing to one redo log file and begins writing to another.

Is there only one redo thread in Oracle?

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.