Add runtime metrics for buffer pools

[mikelaspina]

I'd like to have runtime metrics for buffer pool utilization similar to the existing metrics for memory pools. Data can be gathered from BufferPoolMXBean Something like the following.

runtime.jvm.buffer.pool {type="used",pool="direct"}
runtime.jvm.buffer.pool {type="max",pool="direct"}
runtime.jvm.buffer.pool {type="used",pool="mapped"}
runtime.jvm.buffer.pool {type="max",pool="mapped"}
runtime.jvm.buffer.count {pool="direct"}
runtime.jvm.buffer.count {pool="mapped"}

[cuichenli]

Hey @mikelaspina , I would like to work on this and had a look on how to make it. But I am a little bit confused on what to be watched.

From the BufferPoolMXBean document, we can only get the pool name, count, and memory. While in your example, you still have the type attributes.

So I'm wondering how can we get this type value or it was a mistake? Thanks!

[mikelaspina]

I mapped BufferPoolMXBean.getMemoryUsed() to type=used and BufferPoolMxBean.getTotalCapacity() to type=max. But, in the spirit of #5718, my request should be revised to use separate metrics. Something like process.runtime.jvm.buffer.usage and process.runtime.jvm.buffer.max?