[GitHub] [zookeeper] eolivelli commented on a change in pull request #856: ZOOKEEPER-3319: Add metrics for follower and observer

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eolivelli commented on a change in pull request #856: ZOOKEEPER-3319: Add metrics for follower and observer
URL: https://github.com/apache/zookeeper/pull/856#discussion_r266254342
 
 

 ##########
 File path: zookeeper-server/src/main/java/org/apache/zookeeper/server/Request.java
 ##########
 @@ -305,4 +305,25 @@ public void setException(KeeperException e) {
     public KeeperException getException() {
         return e;
     }
+
+    public void logLatency(ServerMetrics metric, String key, long currentTime) {
+        if (hdr != null) {
+            /* Request header is created by leader. If there is clock drift
+             * latency might be negative. Headers use wall time, not
+             * CLOCK_MONOTONIC.
+             */
+            long latency = currentTime - hdr.getTime();
+            if (latency > 0) {
+                if (key != null) {
+                    metric.add(key, latency);
 
 Review comment:
   I can't understand this point.
   
   Is key optional?
   I am thinking about the new API, I would like to make it explicit in the new API what is the behavior of not using the key.

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