eolivelli commented on issue #840:  ZOOKEEPER-3143 Pluggable metrics system for 
ZooKeeper - Data Collection on Server
URL: https://github.com/apache/zookeeper/pull/840#issuecomment-471690802
 
 
   @jhuan31
   I think that it is better to port all of your stuff from Facebook.
   
   I have sent this patch for you Facebook friends in order to see how the 
MetricsProvider system will be, and to get feedback from the community.
   
   Regarding static vs instance.
   For the server side we could use the static approach. 
   problems:
   - You won't be able to test metrics while starting more than one server  
inside the same jvm
   - You must not cache references to the global 'metrics' object because all 
of the references must always access the global mutable reference, so this 
approach may be more error prone
   
   On the client side we can't go with the 'static' way because inside the same 
jvm/classloader you may have more than one client (think for instance to having 
a hbase client + one curator client...) so a static reference will mix metrics 
about different zk clusters
   
   That said if the community prefer the static approach for the server I am 
fine, but I think that having instance variables will ease at least 
maintainability of the codebase (and testability)

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