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Oracle recovery concepts

I’ve published a while ago a twitter thead on some Oracle recovery concepts. For those who are not following twitter, I’m putting the whole thread here:

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How to reformat corrupt blocks which are not part of any segment?

There was a question in . Problem is that there were many corrupt blocks in the system tablespace not belonging to any segment. Both DBV and rman throws errors, backup is filling the v$database_block_corruption with numerous rows. OP asked to see if these blocks can be reinitialized. Also, note 336133.1 is relevant to this issue on hand.

Restoring Controlfile When AUTOBACKUP Fail

Allow me to present the snapshot of a day from the life of John--the DBA at Acme Bank. On this particular day a database John manages crashed entirely and had to be restored from the backup. He takes regular (backupset) RMAN backups to tape. Since everything--including the controlfile--had crashed, John had to first restore the controlfile and then restore the database. The controlfile is always backed up with the backup database command. John was sure of that. However, restore controlfile from autobackup gave the error:

RMAN-06172: no AUTOBACKUP found or specified handle is not a valid copy or piece

Without the controlfile, the recovery was stuck, even though all the valid pieces were there. It was a rather alarming situation. Others would have panicked; but not John. As always, he managed to resolve the situation by completing recovery. Interested to learn how? Read on.

Oracle Database 12c : Some Backup and Recovery Stuff

In a previous post, I had already listed an article on backup and recovery when using the Oracle 12c multitentant option.

In that article I made reference to a restriction when using flashback database against a CDB with a PDB that has had a point in time recovery. I finally got my head round this and posted a note about it here.

What makes a DBA?

I wrote this article as a foreword for the 2007 Apress book “RMAN Recipes for Oracle Database 11g: A Problem-Solution Approach” by Darl Kuhn, Sam Alapati, and Arup Nanda (ISBN 1590598512), and I’m pleased to learn it will be included in the exciting new Apress update “RMAN Recipes for Oracle Database 12c: A Problem-Solution Approach” (ISBN 143024836X), scheduled for 14-Aug 2013 publication, assuming that Oracle Database 12c^H^H^HNextGeneration is released prior to then…

SCN – What, why, and how?

In this blog entry, we will explore the wonderful world of SCNs and how Oracle database uses SCN internally. We will also explore few new bugs and clarify few misconceptions about SCN itself.

What is SCN?

SCN (System Change Number) is a primary mechanism to maintain data consistency in Oracle database. SCN is used primarily in the following areas, of course, this is not a complete list:

Does an UPDATE statement modify the row if the update modifies the column to same value?


If a table column is updated with the same value in a row, does Oracle RDBMS engine modify the data? (or) Does RDBMS engine have an optimization skipping the update, as value of that column is not changing? This was the essence of a question asked in Oracle-l list and I think, it is a good topic for further discussion. Jared Still came up with a fine method to understand this issue measuring redo/undo size. We will explore the same questions with redo log dump method in this blog entry.

Following few lines shows a test case creating a table, an index, and then populating a row in the table.

create table updtest (v1 varchar2(30));

create index updtest_i1 on updtest(v1);

insert into updtest values ('Riyaj');


REDO records and change vectors

Always Check Your Backups

So this is a 2 node RAC cluster on RHEL that was recently upgraded from to Since then clusterware restarts crs every few hours (8 in fact). A little research suggests that this can indicate problems with the automated OCR backup.  The first thing therefore is to check the state of the backups. [server] [...]