I often run my ops like I take care of data; a bit overzealously. Case in point, when setting up a new database, I like to throw on a metric for database size, which gets turned into both a graph for trending, but also an alert on database size. Everyone is always on board with trending database size in a graph, but the alert is one people tend to question. This is not entirely without justification.
On a new database, with no data or activity, deciding when to alert is pretty fuzzy. When we set up a new client within our
managed hosting service, I usually just toss up an arbitrary number, like 2GB or something. The idea isn’t that a 2GB database is a problem, it’s that when we cross 2GB, we should probably take a look at the trending graph and do a projection. Depending on how things look, we’ll bump up the threshold on the alert to a new level, based on when we think we might want to look at things again. For example, in this graph we take a month long sample, and then project it out for three months. We can then set a new threshold somewhere along that line.
While this is good for capacity planning, there’s more that can be gained from this process. The act of alerting forces us to pay attention. And if we get notices before our expectations, we go back in and re-evaluate the data patterns. Of course, some times people will question this. Getting a notice that your database has passed 4GB can seem pointless when you have 100+ GB of free space on your disks. And besides, isn’t that what free space monitors are for?
Here is a graph of another of our clients database growth. Their data size is not particularly large (don’t confuse scalability with size; it doesn’t take a large database to have scalability issues), but what’s important is that we kept getting notices that the size was growing, and when talking with the developers, no one thought it should be growing at nearly this rate. Eventually we were able to track down the problem to purging job that had gone awry. Once that was fixed, the growth pattern leveled off completely (and the database size returned to the tiny amount that was expected!)
