Oracle compact table

Surely more than once have deleted records from a table in large quantities, perhaps millions. Once this is done it expected would be a reduction of the space used in the tablespaces, but it does not. Extensions but remain free to use the given table, can not use another table.

After the removal of millions of records, you must compact the table to return to tablespace free space once done we can even reduce the size of the datafiles without meeting the limitation imposed by the HIGH WATER MARK (maximum size reached by the objects within a datafile).

Suppose the table:

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Oracle update undo, Massive updates that can generate problems with UNDO tablespace

It is not the first time that I see the need to run a DML which it actually updates many rows, this can be a problem because the UNDO tablespace is not infinite (and not should be).

Recently I had to run an update:

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