In many applications, it seems that performance often falls off a cliff at some point because no one is planning for capacity increases. Everyone talks about the potential load on the system when it's first being built. However since we often over-buy hardware, we rarely monitor the load until something goes wrong.
I was reminded up this with a write-up from Simon Sabin recently that examined a lesson on capacity planning from FourSquare. Apparently FourSquare had some capacity issues with their MongoDB server. Despite the realization that they were growing and the addition of a second node to their database, they didn't learn the lesson and didn't add a third or fourth node until they were over capacity.
Most of us don't experience this type of hyper-growth in our systems. The majority of applications I've seen have undergone a quick growth in load at some point, but then leveled off to a steady, or slowly growing load on the system. However that doesn't necessarily change the planning needed for growth. It just means that you need to grow your system at different times than if you were doubling in size every few months.
A solid monitoring plan, and buy-in from management that you will periodically need to upgrade your servers, is necessary. Typically you will add storage over time, perhaps RAM, and potentially new CPUs or servers. You might not be able to exactly predict when you will have performance issues, but you can plan for issues. You can proactively let management know that space is running low, or that you may run into issues if data sets continue to grow in size.
Funding is often hard to get, but by preparing people in advance that your database will need improvements over time, you are more likely to be able to respond quickly when there are performance issues.
Steve Jones
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