Oracle's serializable transactions cannot be serialized

Question

I'm new to oracle. Here is my understanding of oracle's serializable transactions. Feel free to correct me if i'm wrong.
In my option, the serializable transactions that oracle supports cannot always be serialized.
Oracle suports serializable transactions by ensuring a serializable transaction cannot modify rows changed by other transactions after the serializable transaction began. (Oracle7 Server Concepts Manual, Data Concurrency).
However this constraint doesn't ensure two transactions can be serialized. For example, consider a table A that has two columns: rowid and num.
A has two rows:
rowid num
1 1
2 2
There are two oracle serializable transactions (T1 and T2) defined as follows.
T1
read row 1 from table A into r1
if (r1.num == 1) {
update num of row 2 to 100
commit;
T2
read row 2 from A into r2
if (r2.num == 2) {
update num of row 1 to 100
commit;
Note: row i refers to the row in the table A that has rowid equal to i, for i=1, 2
Consider the following senario:
T1: read (1, 1)
T1: write (2, 100)
T2: read (2, 2)
T2: write(1, 100)
T1: commit
T2: commit
In oracle, the senario above will get executed without any error.
After T1 and T2 commit, the table A has the following rows:
rowid value
1 100
2 100
However, if you serialize T1 and T2, the table A can only be either
rowid value
1 1
2 100
if T1 runs before T2;
or
rowid value
1 100
2 2
if T2 runs before T1.
The conclusion is that serializable transactions in Oracle cannot always be serialized.
Anything wrong in my example?
Thanks
null

Answer 1

Note on the line
46 if (result == null)
47 {
48 String MontoDocumento1 = (String) vo.getCurrentRow (). GetAttribute ("MontoDocumento");
49 String redondeado1 = Round (MontoDocumento1);
50 if (redondeado1.equals ("Y"))
51 { ........
I call a number then convert to string:
String MontoDocumento1 = (String) vo.getCurrentRow (). GetAttribute("MontoDocumento");
and then pass it to double:
Double.valueOf double v_number = (number). doubleValue ();
in my function:
Rounding public String (String number)
Return String;
Double.valueOf double v_number = (number). doubleValue ();
if (v_number == (Math.rint (v_number * 100) / 100))
return = "Y";
else
return = "N";
return return;
Which brings me back a string with the value Y or N.
Thanks if you could help me
Edited by: 917616 on 29/02/2012 07:16 AM