In "classic" NAV when there is a performance issue, say with a big transaction table e.g. "G/L Entry", I will run a SQL database query analyser, and find out what index key fields I need to add to GLEntry table. And this normally will address the problem. Until, some other usage trend comes along. Then I will rinse and repeat.
I just realised that in Dynamics BC online, this is no longer possible. (Please correct me if I'm wrong here...). In Dynamics BC Online, you cannot added key index fields (or sum index fields) that has your extended fields along with standard NAV fields. And if this is true, this is a deal breaker for big enterprise companies planning on jumping on the dynamics bc cloud bandwagon. This is perfectly fine for small to medium companies.