@gianm gauge `emitter/buffers/failed` and `emitter/buffers/totalAllocated` metrics proved to be very inconvenient in practice: they are not additive across a fleet of nodes, are randomly reset when a JVM restarts (that may be completely independent from metrics emitting issues). Regarding [problem identification](https://github.com/apache/incubator-druid/pull/4973#issuecomment-338119125), `emitter/buffers/dropped` serves this well.
Currently in this PR I added `/delta` vs. `/total` metrics, but if there are no objections I would remove `/total` and so align `emitter/buffers/allocated` and `/failed` with `/dropped` and `/events/emitted` which are already delta-only.
Roman Leventov
Clint Wylie