Undo segments in a normal tablespace?

From: Paul Houghton <Paul.Houghton@xxxxxxxxxxxxxxx>
To: Oracle L <oracle-l@xxxxxxxxxxxxx>
Date: Wed, 19 Mar 2014 16:03:20 +0000

We were being slightly silly and running a SQL*Plus script to truncate a
load of tables and load them (insert into table select ... from
other_table) in parallel over and over again, starting some new scripts
before the previous one could complete. 

What confused me is that the tablespace was filling up (We got an
enterpise manager alert). Looking in the tablespace there were a number
of segments like:

SQL>  select segment_name, segment_type, trunc(bytes/1048576) as m from
dba_segments where bytes> 104857600 order by bytes

  ...
  SYS_LOB0001312649C00007$$              LOBSEGMENT               2279
  SYS_LOB0000911233C00007$$              LOBSEGMENT               2311
  _SYSSMU209_2979571356$                 TYPE2 UNDO               2346
  XXXXX_TRN_DETAIL                       TABLE                    2357
  SYS_LOB0001158165C00007$$              LOBSEGMENT               2458
  XXXXX_CS_SCTY_TMP                      TABLE                    2636
  _SYSSMU1_1245196837$                   TYPE2 UNDO               2699
  XXXXXMM_SCTN_DATA                      TABLE                    2813
  XXXXX_EMAILCOM_INF                     TABLE                    2985
  XXXXXIT_CALC_TBL                       TABLE                    3088
  _SYSSMU39_1215612372$                  TYPE2 UNDO               3137
  ...


What is TYPE2 UNDO, and how does it end up in a normal tablespace?

Thanks

PaulH

Follow-Ups:
- RE: Undo segments in a normal tablespace?
  - From: Jonathan Lewis

Undo segments in a normal tablespace?

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