We have successfully upgraded Oracle 11g to Oracle 12c. So far it's been going well. But We noticed one problem, queries made for Oracle's constraint tables (ALL_CONS_COLUMNS and ALL_CONSTRAINTS) are really slow compared to 11g.
When We used 11g, there was no problem at all. The query finished in less than one second but in 12c it is at least 4 times slower. It is affecting all applications We have and even though there's a workaround (application side), ideally, You'd expect the same performance between 11g and 12c.
We have also tried to measure the query cost using Toad. On 12c, the cost is much smaller than 11g. Could this be affecting the query time? Is there anything I can try to solve this problem?
PS : Any other queries made for another tables are okay. Performance wise, there's little to no difference between 11g and 12c.
Any feedback is welcomed. Thank you very much.