How to subsequently change ERROR_ON_OVERLAP_TIME parameter in PL/SQL?

Question

Hi All!
I have a problem considering the ERROR_ON_OVERLAP_TIME session parameter.
I would like to change it from the inside of a PL/SQL block.
It simply works this way:
DECLARE
BEGIN
EXECUTE IMMEDIATE 'ALTER SESSION SET ERROR_ON_OVERLAP_TIME=TRUE';
END;
And that is fine. Try to run the following code subsequently:
set serveroutput on
DECLARE
l_date DATE;
BEGIN
EXECUTE IMMEDIATE 'ALTER SESSION SET ERROR_ON_OVERLAP_TIME=FALSE';
dbms_output.put_line('01 '||sysdate);
l_date:=CAST(from_tz(CAST(TO_DATE('2010.10.31. 02:00:00', 'YYYY.MM.DD. HH24:MI:SS') AS TIMESTAMP), 'Europe/Budapest') AT TIME ZONE 'UTC' AS DATE);
dbms_output.put_line('02 '||sysdate);
EXECUTE IMMEDIATE 'ALTER SESSION SET ERROR_ON_OVERLAP_TIME=TRUE';
dbms_output.put_line('03 '||sysdate);
END;
Once it raises an error as the parameter was set to true, the next time it does not.
This is probably because PL/SQL is not as structured as it is supposed to be.
My guess is that l_date is calculated first, and after it is done, the pl/sql engine starts to evaluate and execute other things such as alter sessions.
So anyone could help me how to solve this problem? I tried several things to overcome this problem (functions, exception branches, etc), but none of them worked.
Any help would be much appriciated. Thanks in advance,
bernyo

Answer 1

The problem still exists. Please take a look at the following example:
Run:
ALTER SESSION SET ERROR_ON_OVERLAP_TIME=FALSE;
At this point the parameter is set to false.Run the followin PL/SQL block:
DECLARE
l_date DATE;
BEGIN
EXECUTE IMMEDIATE 'ALTER SESSION SET ERROR_ON_OVERLAP_TIME=TRUE';
dbms_output.put_line('01 '||sysdate);
l_date:=CAST(from_tz(CAST(TO_DATE('2010.10.31. 02:00:00', 'YYYY.MM.DD. HH24:MI:SS') AS TIMESTAMP), 'Europe/Budapest') AT TIME ZONE 'UTC' AS DATE);
dbms_output.put_line('02 '||sysdate);
EXECUTE IMMEDIATE 'ALTER SESSION SET ERROR_ON_OVERLAP_TIME=FALSE';
dbms_output.put_line('03 '||sysdate);
END;
It does not raise an exception! Why? It should, because the parameter is supposed to be changed by the time the l_date value is assigned, but it is not.
So how should I handle this? It seems to me that this is quite a buggy feature.
Just to see my point check out the following script:
ALTER SESSION SET ERROR_ON_OVERLAP_TIME=TRUE;
SELECT CAST(from_tz(CAST(TO_DATE('2010.10.31. 02:00:00', 'YYYY.MM.DD. HH24:MI:SS') AS TIMESTAMP), 'Europe/Budapest') AT TIME ZONE 'UTC' AS DATE) FROM DUAL;
It raises an exception, as should the PL/SQL block.
Any help is much appriciated.
Thanks,
bernyo