— Clean environment
 drop table gtt;
 drop table gtt
            *
ERROR at line 1:
ORA-00942: table or view does not exist

— Global temporary – preserve rows
create global temporary table gtt ( x int ) on commit preserve rows;
Table created.

— Keeps information until the end of the user session
select duration from user_tables where table_name = ‘GTT’;
DURATION
—————
SYS$SESSION

— Insert one row
insert into gtt values(1);
1 row created.

— Creates a TO lock
select sid, type, id1, id2, lmode from v$lock where id1=(select object_id from all_objects where object_name=’GTT’);
       SID TY        ID1        ID2      LMODE
———- — ———- ———- ———-
      4343 TO     403115          1          3

— Commit transaction
commit;
Commit complete.

— TO lock continues…
select sid, type, id1, id2, lmode from v$lock where id1=(select object_id from all_objects where object_name=’GTT’);
       SID TY        ID1        ID2      LMODE
———- — ———- ———- ———-
      4343 TO     403115          1          3

— Any user that tries to change the table
— Will receive: ORA-14450: attempt to access a transactional temp table already in use
alter table gtt add (y int);
alter table gtt add (y int)
*
ERROR at line 1:
ORA-14450: attempt to access a transactional temp table already in use

— Only after doing truncate
truncate table gtt;
Table truncated.

— TO lock disappears
select * from v$lock where id1=(select object_id from all_objects where object_name=’GTT’);
no rows selected

— With a global temporary table delete rows
drop table gtt;
Table dropped.

create global temporary table gtt ( x int ) on commit delete rows;
Table created.

— The duration is at transaction level
select duration from user_tables where table_name = ‘GTT’;
DURATION
—————
SYS$TRANSACTION

— Insert one row
insert into gtt values(1);
1 row created.

— Creates a TO lock
select sid, type, id1, id2, lmode from v$lock where id1=(select object_id from all_objects where object_name=’GTT’);
       SID TY        ID1        ID2      LMODE
———- — ———- ———- ———-
      4343 TO     403116          1          3

— That disappears as soon as you commit the transaction
commit;
Commit complete.

select sid, type, id1, id2, lmode from v$lock where id1=(select object_id from all_objects where object_name=’GTT’);
no rows selected

— Clean up environment
drop table gtt;
Table dropped.

For instance the ones running for more than 12hours:

select ‘alter system kill session ”’||s.sid||’,’||s.serial#||”’ immediate;’,
s.osuser,s.machine,s.module, CEIL(24*(SYSDATE-t.START_DATE))
from v$session s, v$transaction t
WHERE S.SADDR=T.SES_ADDR
and CEIL(24*(SYSDATE-t.START_DATE))>12;