HADOOP-16398 added exporter for hadoop metrics to prometheus. But some of metrics can't be exported validly. For example like these metrics,
queue metrics for ResourceManager It always exported only one queue's metric because PrometheusMetricsSink$metricLines only cache one metric if theses metrics have the same name no matter these metrics has different metric tags.
rpc metrics for Namenode Namenode may have rpc metrics with multi port like service-rpc. But because the same reason as Issue 1, it wiil lost some rpc metrics if we use PrometheusSink.
3. TopMetrics for Namenode
org.apache.hadoop.hdfs.server.namenode.top.metrics.TopMetrics is a special metric. And I think It is essentially a Summary metric type. TopMetrics record name will according to different user and op , which means that these metric will always exist in PrometheusMetricsSink$metricLines and it may cause the risk of its memory leak. We e need to treat it special.