[orf]

When it comes to shared resources like a database cluster, you’re making the assumption that usage is correlated with number of connections.

Is this always true? Typically the shared resources you care about are CPU, memory and disk. I would say an application issuing fewer, much heavier queries is using the shared resource more than an application that issues more really simple queries. And this doesn’t correlate much to disk usage right?

There isn’t really a good solution to this. You can use a combination of query sampling and per-app databases to correlate this better.

Great post though, this is something we’ve been dealing and experimenting with recently.

[logicfiction]

Your observations are correct. I wouldn’t portray it as an ideal system, just best effort. In the end we care more about the finer details being good funnels to follow up on rather than being exact. We know our real costs of resources, which is important for finance and budget. And then we have the approximate attributions from the sampling which narrow things down enough to focus diagnosis when needed.

I would have to read more into how it intercepts some of our database calls to confirm if it tries to weight for execution time where it wires into database client code, which is probably useful and could help to a degree to approximate utilization.

I think in practice it’s a bit uncommon for the heaviest user to also be a sparse user in terms of volume. But I can also admit there are quirks to how it samples and I once personally spent a couple days tracking down a surprising cost of an application I owned only to later confirm it was a data flaw in how we were doing this sampled attribution (in this case the heaviest users were un-instrumented infra processes that can’t just wire in our java cost attribution library, making it artificially look like my app was the heaviest user).