oracle dba : LUSENET : DBAzine : One Thread

Q1:what is the difference between undo segments or tablespaces and redo log files also whether redo log files resides in undo tablespaces.? Q2 :how can we relate segments and tables? Q3:when we create tables then whether these tables are actually created in segments and whether their resides in data files or not?

-- yasser afzal khan (, June 04, 2003


You sound like you really need some background info about Oracle.

Q1 - UNDO vs REDO. REDO LOGS are just that, sequential datasets. UNDO segments are just that, tablespaces. REDO logs let you recover forward. UNDO lets you recover backward, for example in the event of a transaction that issues a ROLLBACK. UNDO Segments last only for the length of time of the transaction. REDO logs, if you off load them, will stay around forever. Q2 - segments and tables. tables live in tablespaces. tablespaces are suppoorted by datasets (files). Internally in Oracle, tables are allocated in SEGMENTs. check the SEGSIZE parm on your CREATE statments and in the dictionary.

Q3 - yes, the tables live in datafiles. but are allocated by segments. Tell your boss you need some basic Oracle education. Oracle confuses EVERYTHING because they try to be everything to everyone on every platform.

-- Steve Pratt (, August 30, 2004.

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