10 Things You Should Know About Running MongoDB At Scale
It turns out that in real-life large deployments the biggest impact to performance is how well the schema design fits with the application needs. Second biggest impact is from lack of indexes or wrong indexes or way too many indexes. But even when the schema design is perfect and indexes are optimal, it is the disk IO throughput capacity that ends up being the next limiting factor, especially to the write throughput. Insufficient RAM will cause a lot of page faulting and add pressure to the disk IO, more on RAM needs later.