Sanphot too old - read consistiency

Question

Hello.
I think this is a basic thing (release 8.1.7.4). I must say I don't know how rollback segments really work.
A table, where new records are continuously inserted and the old ones can be updated in short transactions, should be purged every day by deleting old records.
This purge has never been done and as a result it has now almost 4 million records, and when I launch the stored procedure that deletes the old records I get the "snapshot too old" error because of the read consistency.
If I launch the procedure after stopping the application that inserts and updates in the table, then I don't get the error. I guess the problem is that meanwhile the procedure is being executed other transactions also need to use rollback segments so that the rollback segment space that the snapshot needs isn't enough. Do you think this is the problem?
If this is the case then I suppose that the only solution is increasing the size of the only datafile of the only tablespace for my 4 rollback segments. Am I wrong?
One possible solution could be not deleting the whole table at once but only a few records? Would this work? Why when I try "select count(*) from my_table where rownum = 1" I also get "snapshot too old" when other transactions are running?
Why do I get the same error in two different databases, in the first the size of the datafile of the undo tablespace is 2GB whilst in the second it is only 2MB? How can I know how big the datafile has to be?
(One more question:
- What is a discrete transaction?)
I'm a developer, not a dba, but don't tell me to ask my dba because it isn't that easy. Thanks in advance.
Thaks in advance.

Answer 1

Try increasing the undo retention time