Guys, calm down!
Liacat, since you know you are junior, be a bit more modes. Davey is an EXPERT and the fact that you are certified does not makes you bigger expert. Most of people here are certified and do not even mention that.
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SQL> alter session set undo_suppress_errors = true;
Session altered.
SQL> set transaction use rollback segment SYSSMU1$;
Transaction set.
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That was the biggest nonesnse I have seen in that forum, so please realise you have much to learn before starting to talk like expert.
However I have to admit you are right for some things
1) ora-01555 is a night mare - as you can see NOONE gives specific recommendation although some talks like if they know what the reason could be but it is just too comlicated to explain to us, normal people
2) Fetch across commit was a good point. If the issue is 100% reproducable, that's most probably the case
At the end of the day the poster seems lost interest in that, since he is neither postin nor answering anymore