Metrics endpoint is slow

[jayme-github]

I've added jmx_exporter to a WildFly 10 setup and notices that the /metrics endpoint is pretty slow (in relation to various other endpoints from applications and exporters). For me /metrics returns data in around 7-10 seconds (without any user load on the server) and would occasionally exceed the prometheus default scrape timeout of 10 seconds.

If this is normal (I'm new to all this Java/JMX/WildFly stuff) a short note in the readme would be cool (at least for people like me 😃 ).

[brian-brazil]

This is normal, JMX is not particularly efficient.

[finkr]

As mentioned by Brian Brazil: JMX is not particularly efficient.

Using whitelistObjectNames, It is often possible to dramatically speed-up things (dropped from 15 seconds to 0.9s. in my use case).
See -> #284