Ask HN: What libraries you use for Application Performance Monitoring?

We are building a java backend service. Would like to ask the community how do you measure the performance of your service. How do you track exception rates (if any), no of tasks completed per minute, etc. Basically we want to define custom metrics, emitted periodically from the service and stored to generate realtime graphs. JMX is a way to get hold of these metrics, however, are there any end-to-end libraries that can help to log, record and generate graphs from this time-series data?

(I am looking for open source alternatives, for using in a commercial app. there is serverDensity but it is paid-subscription based API.)