If you’ve been a DBA long enough, you’ve probably seen multiple cases where certain SQL queries just refuse to cooperate.
I.e. you KNOW that the query is supposed to use index IDX1, but ORACLE stubbornly decides to take IDX2. Rats!
The usual suspect here is bad statistics and thus the usual advise is: start re-collecting them. But while this might help, the success is far from guaranteed! Moreover, with a ‘real production’ data statistics collection could take hours (days?) and you already have people screaming about slow performance … In other words, you need to fix the problem NOW and waiting until stats collection maybe fixes the problem a few hours down the road is just not an option!