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Subject [GitHub] [zookeeper] jhuan31 commented on issue #840: ZOOKEEPER-3143 Pluggable metrics system for ZooKeeper - Data Collection on Server
Date Mon, 11 Mar 2019 17:05:00 GMT
jhuan31 commented on issue #840:  ZOOKEEPER-3143 Pluggable metrics system for ZooKeeper - Data
Collection on Server
URL: https://github.com/apache/zookeeper/pull/840#issuecomment-471630416
 
 
   @eolivelli Since you don't think my questions are stupid, so here comes more :)
   
   Could you please give a scenario that a static ServerMetrics variable would cause trouble?
If we default the static variable to NULL_METRICS then nothing would happen before the main
Zookeeper thread starts the metric provider and sets the static variable to the right instance.
After the static variable is set correctly, then the metrics will be reported correctly. Same
behavior as the non-static case. 
   
   The reason we are cautious about switching to non-static serverMetrics is that we have
so many metrics and we need to change the constructor or initialization logic for all classes
that report metrics and classes along the invocation chain from the main thread. It's messy
and error-prone. For example, in this change, the serverMetrics for watchManager is not set.
The unit test will pass because it is set in the tests. But it is not set in the regular execution
path.
   
   Another concern is, if we want to report metrics in a static function, how can it get hold
of the serverMetrics instance?   
   
   Thanks!

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