"What we found is that's more than enough for 99.9 percent of our customers," said Matt Soldo , product manager of Heroku Postgres. However, "we're thinking about how we can support folks who go beyond that," Soldo added.

One potential way is by providing guidance to customers on how they can effectively divide, or "shard" their databases across multiple instances on Heroku, he said.

Heroku charges for its production tiers based on RAM because "Web apps, [available RAM] turns out to be critical for speed," he said. Over time, the cost of networking and storage is going to drop to the point it's "effectively free," he said.

The highest-level database tier now offered by Heroku costs $6,400 per month and provides 68GB of caching.

But the two new tiers were the "number-one requested feature" from Heroku's user base, Soldo said. "Going from zero to $200 per month is a serious jump for certain types of customers."