One of my query got failed with 01555. But I didn't see any reasons for this because ...
undo table space is 180G
undo retention is 2 hours
and the above said query which is running from ETL frame work has a target commit interval for every 100000 rows.
Thou source and target tables are more than 150M each and the whole query SLA is 19 hours still i didn't see any reason to tail with 01555 because the above undo & commit settings.
I have attached the query for your reference and the insert query is just a plain insert.
Please note that, this is the ONLY session running in the database during 01555.
Try hard to get what you like OR you will be forced to like what you get.