Oracle Database Undo space explained

In this blog post I will talk about the basic workings of Automatic Undo Management, which can cause ORA-01555 and ORA-30036 issues.

The scope is Automatic Undo Management used in 10g and 11g, but has to be explicitly set for 9i (UNDO_MANAGEMENT = AUTO). Manual Undo Management is out of scope for this blog.

The Undo tablespace is a normal tablespace like any other, but only Oracle is controlling what is happening inside it.

Undo something

The Undo tablespace is used for several features: ROLLBACK, READ CONSISTENCY and FLASHBACK technology. Continue reading