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Don Burleson Blog 







Oracle UNDO tablespace too full tips

Oracle Database Tips by Donald BurlesonDecember 29, 2015

Question:  After one high DML transaction my UNDO tablespace was almost full and after many days the UNDO tablespace is almost full.  Why first UNDO tablespace being flushed automatically?  Why is my UNDO tablespace remain full after many days while there are not any update transactions?

Answer:  Oracle will manage all UNDO for you.  See my notes on UNDO tablespace size and shrinking.

Oracle keeps the transactions in a circular buffer with the UNDO tablespace.  The UNDO tablespace is not really full!

The UNDO tablespace is special and it is managed internally by Oracle.  The internal undo data is only "logically deleted" instead of being physically deleted.

You only have to worry about UNDO space if you get the error: ORA-01555: Snapshot too old:  rollback segment too small.

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