Q: Impact of use_current_session parameter of dbms_scheduler.run_job

Question

On the 11g db that I have access to, I'm seeing different systimestamp value while running plsql block using
dbms_scheduler.run_job with use_current_session = true and false.
My job looks like following.
dbms_scheduler.create_job(
job_name => 'tk2timestamp_test',
job_type => 'PLSQL_BLOCK',
job_action => 'begin insert into tktest values (systimestamp, to_char(sysdate, ''DD-MON-YYYY HH24:MI:SS''), current_timestamp, localtimestamp, dbtimezone, sessiontimezone); end;',
enabled => true,
auto_drop => false);
I see that UTC time was returned as systimestamp if it is called with true and PST if it is called with false.
In the same session, I get following result with select statement.
select systimestamp, current_timestamp, localtimestamp, dbtimezone, sessiontimezone from dual;
SYSTIMESTAMP CURRENT_TIMESTAMP LOCALTIMESTAMP DBTIMEZONE SESSIONTIM
27-MAR-13 04.05.59.914647 PM +00:00 27-MAR-13 09.05.59.914650 AM -07:00 27-MAR-13 09.05.59.914650 AM +00:00 -07:00
Can any one let me know why this is happening? Why systimestamp value is not PST if use_current_session = true?

Answer 1

Thank you again for your response.
I've got following result.
SQL> SELECT SYSTIMESTAMP FROM dual;
SYSTIMESTAMP
28-MAR-13 07.13.08.556079 PM +00:00
SQL> SELECT SYSTIMESTAMP AT TIME ZONE 'PDB' FROM dual;
SELECT SYSTIMESTAMP AT TIME ZONE 'PDB' FROM dual
ERROR at line 1:
ORA-01882: timezone region not found
SQL> SELECT SESSIONTIMEZONE,CURRENT_TIMESTAMP, LOCALTIMESTAMP FROM dual;
SESSIONTIM CURRENT_TIMESTAMP LOCALTIMESTAMP
-07:00 28-MAR-13 12.13.41.196653 PM -07:00 28-MAR-13 12.13.41.196653 PM
BTW, I have two instances returns the result like this if this information helps.
I've created following table in order to help proving something is changing whether I pass true or false to use_current_session parameter when calling dbms_scheduler.run_job.
create table tktest (tksystimestamp timestamp(6), tktocharsysdate varchar2(100), tkcurrent_timestamp timestamp(6), tklocaltimestamp timestamp(6), tldbtimezone varchar2(100), tksessiontimezone varchar2(100));
Then I created job as following. This job inserts systimestamp,sysdate,current_timestamp,localtimestamp,dbtimezone, and sessiontimezone to above table.
begin
dbms_scheduler.create_job(
job_name => 'tk2timestamp_test',
job_type => 'PLSQL_BLOCK',
job_action => 'begin insert into tktest values (systimestamp, to_char(sysdate, ''DD-MON-YYYY HH24:MI:SS''), current_timestamp, localtimestamp, dbtimezone, sessiontimezone); end;',
enabled => true,
auto_drop => false);
exception
when others then
null;
end;
Run the job using run_job procedure.
exec dbms_scheduler.run_job(job_name => 'tk2timestamp_test',use_current_session => true);
Above inserts following record in tktest.
SYSTIMESTAMP SYSDATE CURRENT_TIMESTAMP LOCALTIMESTAMP DBTZ SESSIONTZ
28-MAR-13 07.04.58.227616 PM 28-MAR-2013 19:04:58 28-MAR-13 07.04.58.227617 PM 28-MAR-13 07.04.58.227617 PM +00:00 +00:00
Run the job using run_job procedure again but use 'use_current_session => false' this time.
Above inserts following record in tktest.
SYSTIMESTAMP SYSDATE CURRENT_TIMESTAMP LOCALTIMESTAMP DBTZ SESSIONTZ
28-MAR-13 12.05.24.150817 PM 28-MAR-2013 12:05:24 28-MAR-13 12.05.24.150819 PM 28-MAR-13 12.05.24.150819 PM +00:00 -07:00
I also run following from the same session.
SQL> select systimestamp, current_timestamp, localtimestamp, dbtimezone, sessiontimezone from dual;
SYSTIMESTAMP CURRENT_TIMESTAMP LOCALTIMESTAMP DBTZ SESSIONTZ
28-MAR-13 07.05.40.640499 PM +00:00 28-MAR-13 12.05.40.640503 PM -07:00 28-MAR-13 12.05.40.640503 PM +00:00 -07:00
So why executing dbms_scheduler.run_job with 'use_current_session => false' causes SEESSIONTIMEZONE to be PST8PDT?
I have an another instance pointing all the time based on UTC and my question is why only above instance is showing result like above and what causes it.
thx.