oracle undo usage

1-- UNDO tablespace current usage / available space
2SELECT a.TABLESPACE_NAME, SIZEMB, USAGEMB, (SIZEMB - USAGEMB) AS FREEMB
3FROM (SELECT round(sum(BYTES) / 1e6) AS SIZEMB, b.TABLESPACE_NAME
4      FROM DBA_DATA_FILES a, DBA_TABLESPACES b
5      WHERE a.TABLESPACE_NAME = b.TABLESPACE_NAME AND b.CONTENTS LIKE 'UNDO'
6      GROUP BY b.TABLESPACE_NAME) a,
7     (SELECT c.TABLESPACE_NAME, sum(BYTES) / 1e6 AS USAGEMB
8      FROM DBA_UNDO_EXTENTS c
9      WHERE STATUS <> 'EXPIRED'
10      GROUP BY c.TABLESPACE_NAME) b
11WHERE a.TABLESPACE_NAME = b.TABLESPACE_NAME;

1-- UNDO tablespace usage per user / session
2SELECT s.SID, s.USERNAME, round(sum(ss.VALUE) / 1e6, 2) AS UNDO_SIZE_MB,
3       sql.ELAPSED_TIME, sql.SQL_TEXT
4FROM V$SESSTAT ss JOIN V$SESSION s ON s.SID = ss.SID
5     JOIN V$STATNAME STAT ON STAT.STATISTIC# = ss.STATISTIC#
6     LEFT JOIN V$SQLAREA sql 
7     	ON s.SQL_ADDRESS = sql.ADDRESS AND s.SQL_HASH_VALUE = sql.HASH_VALUE
8WHERE STAT.NAME = 'undo change vector size' AND s.TYPE <> 'BACKGROUND' 
9  AND s.USERNAME IS NOT NULL AND ss.VALUE >= 0.01 * 1e6
10GROUP BY s.SID, s.USERNAME, sql.ELAPSED_TIME, sql.SQL_TEXT
11ORDER BY s.USERNAME, round(sum(ss.VALUE) / 1e6, 2);