Log in to oracle with DBA user (user having dba rights)

How to list sessions to a database?

SELECT MACHINE, STATE, STATUS, USERNAME, SCHEMANAME, OSUSER, PROGRAM, LOGON_TIME from V$SESSION

How to monitor used temp tablespace?

SELECT  TABLESPACE_NAME, BYTES_USED, BYTES_FREE from V$TEMP_SPACE_HEADER;
select TABLESPACE_NAME, BYTES_USED/(1024*1024*1024), (BYTES_FREE)/(1024*1024*1024) from V$TEMP_SPACE_HEADER;

Temporary segments

SELECT   A.tablespace_name tablespace, D.mb_total,
         SUM (A.used_blocks * D.block_size) / 1024 / 1024 mb_used,
         D.mb_total - SUM (A.used_blocks * D.block_size) / 1024 / 1024 mb_free
FROM     v$sort_segment A,
         (
         SELECT   B.name, C.block_size, SUM (C.bytes) / 1024 / 1024 mb_total
         FROM     v$tablespace B, v$tempfile C
         WHERE    B.ts#= C.ts#
         GROUP BY B.name, C.block_size
         ) D
WHERE    A.tablespace_name = D.name
GROUP by A.tablespace_name, D.mb_total;

Sort space use by session

SELECT   S.sid || ',' || S.serial# sid_serial, S.username, S.osuser, P.spid, S.module,
         S.program, SUM (T.blocks) * TBS.block_size / 1024 / 1024 mb_used, T.tablespace,
         COUNT(*) sort_ops
FROM     v$sort_usage T, v$session S, dba_tablespaces TBS, v$process P
WHERE    T.session_addr = S.saddr
AND      S.paddr = P.addr
AND      T.tablespace = TBS.tablespace_name
GROUP BY S.sid, S.serial#, S.username, S.osuser, P.spid, S.module,
         S.program, TBS.block_size, T.tablespace
ORDER BY sid_serial;

Sort space usage by statement

SELECT   S.sid || ',' || S.serial# sid_serial, S.username,
         T.blocks * TBS.block_size / 1024 / 1024 mb_used, T.tablespace,
         T.sqladdr address, Q.hash_value, Q.sql_text
FROM     v$sort_usage T, v$session S, v$sqlarea Q, dba_tablespaces TBS
WHERE    T.session_addr = S.saddr
AND      T.sqladdr = Q.address (+)
AND      T.tablespace = TBS.tablespace_name
ORDER BY S.sid;

How to see what DB/Schema is doing?

SELECT S.USERNAME||'('||s.sid||')-'||s.osuser UNAM
,s.program||'-'||s.terminal||'('||s.machine||')' PROG
,s.sid||'/'||s.serial# sid
,s.status "Status",p.spid
,sql_text sqltext
from v$sqltext_with_newlines t,V$SESSION s , v$process p
where t.address =s.sql_address
and p.addr=s.paddr(+)
and t.hash_value = s.sql_hash_value
and s.machine like '%VMCAST-ANA-ST-4%'
order by s.sid,t.piece